Intermediate Food Technology interview questions

150 questions with answers (FDT-151 to FDT-300). Try each one aloud before reading the answer.

Food Chemistry

FDT-151 · What is the Maillard reaction?

A non-enzymatic browning reaction between reducing sugars and amino groups (amino acids, proteins) during heating. It proceeds via Amadori products to melanoidins, giving the brown colour and roasted flavours of bread crust, coffee and roasted meat.

FDT-152 · Which factors accelerate the Maillard reaction?

High temperature, intermediate water activity (about 0.6–0.8), mildly alkaline pH, reducing sugars (pentoses react faster than hexoses) and lysine-rich proteins. Low aw, acidity and low temperature slow it.

FDT-153 · How is acrylamide formed in food?

Mainly from asparagine reacting with reducing sugars through the Maillard pathway at high temperatures (above about 120 °C) in low-moisture foods such as fries, chips and coffee. Blanching, asparaginase treatment and lower frying temperatures reduce it.

FDT-154 · What is Strecker degradation?

A Maillard side reaction in which α-dicarbonyl compounds deaminate and decarboxylate amino acids to form aldehydes (Strecker aldehydes) with one less carbon, plus CO₂ and aminoketones. It contributes key aroma compounds.

FDT-155 · Explain the mechanism of lipid autoxidation.

A free-radical chain reaction. In initiation, a hydrogen is abstracted from an unsaturated fatty acid. In propagation, the lipid radical reacts with O₂ to form a peroxyl radical and hydroperoxides. In termination, radicals combine. Hydroperoxides break down into volatile aldehydes and ketones that cause rancid flavour.

FDT-156 · What do peroxide value and free fatty acid value indicate?

Peroxide value (meq O₂/kg) measures primary oxidation products (hydroperoxides) and reflects early oxidative rancidity. FFA (as % oleic acid) or acid value measures hydrolytic rancidity.

FDT-157 · What do iodine value and saponification value indicate?

Iodine value (g I₂ absorbed per 100 g fat) measures unsaturation. Saponification value (mg KOH to saponify 1 g fat) is inversely related to average fatty-acid chain length, so a higher value means shorter chains.

FDT-158 · What is hydrogenation of oils, and why are trans fats a concern?

Hydrogenation adds hydrogen across double bonds using a nickel catalyst to harden oils. Partial hydrogenation forms trans fatty acids, which raise LDL and lower HDL cholesterol. FSSAI limits industrial trans fat to 2% of total fat in oils and fats and in foods containing them.

FDT-159 · What is interesterification?

Rearranging fatty acids on the glycerol backbone, chemically (sodium methoxide) or enzymatically (lipase), to change melting and crystallisation behaviour without forming trans fats. It is used for margarine and shortening bases.

FDT-160 · How does the HLB value guide emulsifier selection?

HLB (hydrophilic–lipophilic balance) runs from about 0 to 20. Low-HLB emulsifiers (about 3–6) favour water-in-oil emulsions such as butter and margarine. High-HLB emulsifiers (about 8–18) favour oil-in-water emulsions such as mayonnaise and beverages.

FDT-161 · How does pH affect anthocyanin colour?

Anthocyanins are red at low pH (flavylium cation), shift to colourless or purple near neutral pH and turn blue to green and unstable at alkaline pH. This is why red cabbage changes colour with cooking-water pH.

FDT-162 · Why do green vegetables turn olive-brown on cooking?

Heat and acids released from tissues replace magnesium in chlorophyll with H⁺, forming olive-brown pheophytin. Short cooking, an open lid to vent volatile acids and avoiding acid help retain the green colour.

FDT-163 · What is starch retrogradation, and where does it matter?

Reassociation and recrystallisation of amylose and amylopectin chains after gelatinised starch cools. It causes bread staling, syneresis in gels and the firming of cooked rice, and it forms resistant starch type 3.

Food Microbiology

FDT-164 · What are the intrinsic and extrinsic factors affecting microbial growth?

Intrinsic factors belong to the food: pH, aw, redox potential, nutrients, antimicrobial constituents and biological structure. Extrinsic factors belong to the environment: temperature, relative humidity, gas atmosphere and other microbes present.

FDT-165 · Why is *Listeria monocytogenes* a major concern in ready-to-eat foods?

It is psychrotrophic and grows at refrigeration temperatures. It tolerates salt, forms biofilms in plants and causes listeriosis, which has high mortality in pregnant women, newborns, the elderly and immunocompromised people. Post-process contamination of RTE deli meats, soft cheeses and smoked fish is the key risk.

FDT-166 · Why does *Staphylococcus aureus* food poisoning occur even after reheating?

*S. aureus* grows in handled foods held warm and produces enterotoxins that are heat-stable. Reheating kills the cells but does not destroy the toxin, which causes rapid vomiting within about 1–6 hours.

FDT-167 · Why is *Bacillus cereus* linked to cooked rice?

Its spores survive cooking. If rice is held warm or cooled slowly, they germinate and produce a heat-stable emetic toxin (cereulide) that reheating does not destroy. Rapid cooling and hot holding above 60 °C prevent this.

FDT-168 · What is *Clostridium perfringens* food poisoning?

A toxico-infection from large numbers of vegetative cells in meat dishes, gravies or stews that were cooled slowly or held warm. The cells sporulate in the gut and release enterotoxin, causing diarrhoea and cramps 8–16 hours after eating.

FDT-169 · What is the significance of *E. coli* O157:H7?

A Shiga-toxin-producing *E. coli* (STEC) with a very low infective dose. It causes haemorrhagic colitis and haemolytic uraemic syndrome. Sources include undercooked ground beef, raw milk, sprouts and contaminated produce.

FDT-170 · How does the MPN method work?

Most Probable Number is a statistical estimate. Replicate tubes at serial dilutions are inoculated, positive tubes (e.g. gas production for coliforms) are counted, and the count is read from MPN tables. It suits low counts and liquid samples.

FDT-171 · What are rapid methods in food microbiology?

Methods faster than conventional culture, such as PCR and real-time PCR, ELISA immunoassays, ATP bioluminescence for hygiene, impedance, lateral-flow tests, chromogenic media and MALDI-TOF for identification.

FDT-172 · What is a biofilm and why is it a problem in food plants?

A community of microbes attached to a surface and embedded in self-produced extracellular polymers. Biofilms resist cleaning and sanitisers, shelter pathogens like *Listeria* and cause recurring contamination of product.

FDT-173 · What is the generation time of bacteria, and how is it calculated?

The time for a population to double during exponential growth. g = t ÷ n, where the number of generations n = (log N − log N₀) ÷ log 2 = 3.3 × log(N/N₀).

FDT-174 · What are the main spoilage organisms in different food categories?

Pseudomonads spoil chilled meat, fish and milk. Lactic acid bacteria spoil vacuum-packed meats and beverages. Yeasts and moulds spoil fruits, jams, bread and other low-aw or acidic foods. Spore-formers spoil canned and heat-treated foods.

FDT-175 · What are aflatoxins and how are they controlled?

Carcinogenic mycotoxins (B1, B2, G1, G2; M1 in milk) produced by *Aspergillus flavus* and *A. parasiticus* in groundnuts, maize, spices and nuts. Control relies on drying grain quickly to safe moisture, cool dry storage, sorting damaged kernels and testing against FSSAI limits.

FDT-176 · Why are viruses like norovirus and hepatitis A important in food safety?

They do not grow in food but are highly infectious at low doses. They spread through infected food handlers, contaminated shellfish and produce, and they resist many sanitisers. Control depends on hand hygiene, excluding ill workers and using safe water.

Food Preservation

FDT-177 · What is water activity (aw)?

The ratio of the water vapour pressure of a food to that of pure water at the same temperature (aw = p/p₀, equal to ERH/100). It measures water available for microbes and reactions. Most bacteria need aw above about 0.91, most yeasts 0.88 and most moulds 0.80.

FDT-178 · What is a moisture sorption isotherm?

A curve of equilibrium moisture content against aw at constant temperature. It is usually sigmoid (type II) for foods. It shows monolayer water, hysteresis between adsorption and desorption, and guides drying end-points and packaging.

FDT-179 · What are intermediate moisture foods (IMF)?

Foods with aw of about 0.6–0.9 and moisture of about 10–40%, shelf-stable without refrigeration through humectants (sugar, salt, glycerol), preservatives and acidity. Examples are jams, dried fruits, soft candies and some pet foods.

FDT-180 · How do sodium benzoate and potassium sorbate work, and why does pH matter?

They are weak-acid preservatives whose undissociated form crosses microbial membranes and disrupts metabolism. They work best below their pKa (benzoic about 4.2, sorbic about 4.76), so benzoate suits acidic drinks and sorbate tolerates slightly higher pH.

FDT-181 · How does freezing rate affect food quality?

Fast freezing (e.g. IQF, cryogenic) quickly passes through the zone of maximum ice-crystal formation (about −1 to −5 °C) and forms many small intracellular crystals, preserving texture. Slow freezing forms large extracellular crystals that rupture cells, causing drip loss on thawing.

FDT-182 · What is freezer burn?

Surface dehydration of frozen food by ice sublimation, causing dry, discoloured, tough and oxidised patches. Temperature fluctuations and poorly fitting or permeable packaging make it worse.

FDT-183 · What is IQF?

Individual Quick Freezing: freezing small pieces (peas, shrimp, diced fruit) separately in fluidised-bed or tunnel freezers so they stay free-flowing and freeze fast with good quality.

FDT-184 · What irradiation dose ranges are used for different purposes?

Low dose (under 1 kGy) inhibits sprouting, disinfests insects and delays ripening. Medium dose (1–10 kGy) reduces spoilage and pathogenic microbes (radurization, radicidation). High dose (above 10 kGy) gives sterilization (radappertization) for special uses.

FDT-185 · What is high-pressure processing (HPP)?

A non-thermal method that applies isostatic pressure of about 400–600 MPa for minutes, usually at chilled or ambient temperature. It inactivates vegetative microbes while retaining fresh-like flavour and nutrients. Bacterial spores mostly survive, so low-acid HPP foods must be kept chilled.

FDT-186 · What is pulsed electric field (PEF) processing?

Applying short high-voltage pulses (roughly 10–50 kV/cm) to pumpable foods, which causes electroporation of microbial cell membranes. It is used for mild pasteurization of juices and to improve extraction and cutting of potatoes.

FDT-187 · How does sugar preserve food?

High sugar concentration lowers water activity and creates osmotic stress that dehydrates microbial cells. Jams at about 65–68 °Brix resist most bacteria but can still support osmophilic yeasts and moulds.

FDT-188 · How does refrigeration slow spoilage, and what is the Q₁₀ concept?

Lower temperature slows microbial growth and reaction rates. Q₁₀ is the factor by which a rate rises for every 10 °C increase, typically about 2–3 for chemical spoilage reactions and often higher for microbial growth near the minimum.

FDT-189 · What is the role of nitrite as a preservative beyond colour?

Nitrite inhibits *C. botulinum* outgrowth and toxin formation in cured meats, gives cured flavour and acts as an antioxidant. Its residual levels are restricted because it can form carcinogenic nitrosamines.

Thermal Processing

FDT-190 · Why is pH 4.6 the dividing line in thermal processing?

*Clostridium botulinum* spores cannot germinate and produce toxin at or below pH 4.6. Foods above pH 4.6 need retort sterilization (about F₀ ≥ 3 min). Acid foods need only pasteurization-level treatment against yeasts, moulds and acid-tolerant bacteria.

FDT-191 · What is the botulinum cook?

The minimum process for low-acid canned foods that gives 12 log reductions of *C. botulinum* spores. With D₁₂₁ = 0.21 min, that is F₀ = 12 × 0.21 = 2.52 min, commonly rounded to F₀ ≈ 3 min.

FDT-192 · What is the lethal rate in thermal processing?

L = 10^((T − T_ref)/z): the lethal effect of one minute at temperature T relative to one minute at the reference temperature. At 111.1 °C with z = 10 °C, L = 0.1.

FDT-193 · What is a heat penetration test?

Placing thermocouples at the cold point of filled containers in a retort and recording product temperature over time. The data are used to calculate the delivered lethality and to establish a scheduled process.

FDT-194 · What is a temperature distribution test?

Mapping temperatures throughout an empty or loaded retort with multiple sensors to find the slowest-heating zone and confirm uniformity and venting adequacy before heat penetration studies.

FDT-195 · Why is venting of a steam retort important?

Air trapped in the retort insulates containers and lowers the temperature at a given pressure, causing cold spots and under-processing. Venting removes air so that pressure and temperature correspond to saturated steam.

FDT-196 · What are the types of retorts?

Static batch retorts using steam, water immersion or water spray; agitating retorts (end-over-end or axial rotation) for faster convection heating; and continuous retorts such as hydrostatic towers and reel-and-spiral cookers.

FDT-197 · Why is overpressure needed when retorting pouches and trays?

During heating, internal pressure from expanding headspace gas and steam can exceed the external pressure and burst seals or deform packs. Air overpressure in steam–air or water retorts balances this, especially during cooling.

FDT-198 · What is ohmic heating?

Passing alternating electric current directly through a conductive food so it heats volumetrically from its own electrical resistance. It heats particles and liquid more uniformly, which suits particulate foods in aseptic processing.

FDT-199 · How does microwave heating work?

Microwaves (2450 MHz domestic, 915 MHz often industrial) make polar molecules such as water rotate and ions oscillate (dipolar and ionic heating), generating heat volumetrically. Heating can be uneven because of standing waves, edge effects and differences between ice and water.

FDT-200 · What is a pasteurization unit (PU) in beer processing?

One PU is the lethal effect of 1 minute at 60 °C. Tunnel-pasteurised beer typically receives about 15–25 PU, calculated as PU = t × 1.393^(T − 60).

FDT-201 · Why is cooling after retorting critical?

Rapid cooling to about 38–40 °C stops cooking to protect quality and prevents thermophilic spore growth. Leaving cans slightly warm lets surface water evaporate to prevent rust. Cooling water must be chlorinated because seams can draw in water while cooling.

FDT-202 · What is flat sour spoilage?

Spoilage of low-acid canned foods by thermophilic spore-formers such as *Geobacillus stearothermophilus*. They produce acid without gas, so the cans look normal but the contents are sour. Slow cooling or hot storage favours it.

Dairy Technology

FDT-203 · What is UHT processing of milk?

Heating milk to about 135–150 °C for a few seconds by direct steam injection or infusion, or by indirect heat exchangers, then packing aseptically. This gives commercially sterile milk stable for months at ambient temperature.

FDT-204 · What is the difference between direct and indirect UHT heating?

Direct heating injects steam into milk or infuses milk into steam, heating it almost instantly. The added water is removed by flash cooling, giving less cooked flavour. Indirect heating uses plate or tubular exchangers, which is simpler and regenerative but has longer heating and more fouling and cooked taste.

FDT-205 · What is the alkaline phosphatase test?

A test for adequate pasteurization. Alkaline phosphatase is slightly more heat-resistant than milk's non-spore-forming pathogens, so its absence after HTST indicates proper heating and no raw-milk contamination.

FDT-206 · What is the MBRT test?

Methylene Blue Reduction Test: an indirect measure of the bacterial load of raw milk. Bacterial metabolism removes oxygen and decolourises the dye, so a shorter reduction time means poorer microbial quality.

FDT-207 · What are platform tests for raw milk?

Quick tests at reception: organoleptic check, temperature, clot-on-boiling (COB), alcohol test, lactometer reading, fat and SNF, titratable acidity and adulterant screening for urea, starch, detergents and neutralisers.

FDT-208 · What is titratable acidity in milk?

The acidity measured by titrating with 0.1 N NaOH using phenolphthalein, expressed as % lactic acid. Fresh cow milk shows about 0.13–0.15% because of its natural casein, phosphates and citrates (apparent acidity). Higher values indicate bacterial souring.

FDT-209 · How are fat and SNF estimated in milk using a lactometer?

Fat is measured by the Gerber method. SNF is calculated from the corrected lactometer reading and fat using an empirical formula such as Richmond's: SNF% ≈ CLR/4 + 0.2 × Fat + 0.14.

FDT-210 · How is cheese made?

Standardised milk is pasteurised, inoculated with starter, and coagulated with rennet. The curd is cut, cooked and stirred to expel whey, then drained, salted, moulded and pressed, and ripened for flavour and texture.

FDT-211 · How is butter made?

Cream (about 35–40% fat) is pasteurised, cooled and aged to crystallise fat, then churned. Churning inverts the oil-in-water emulsion into a water-in-oil one. Buttermilk is drained, and the butter is washed, salted and worked. FSSAI requires at least 80% milk fat.

FDT-212 · How is milk powder made?

Milk is standardised, preheated, concentrated in a falling-film evaporator to about 45–50% solids, then spray dried. It may be agglomerated or instantised. Preheat intensity determines whether the powder is low-, medium- or high-heat.

FDT-213 · How is khoa made, and what are its types?

Milk is heated in an open pan with constant scraping to evaporate water to about 65–70% solids. The types are pindi (hard, for burfi), dhap (soft, for gulab jamun) and danedar (granular, for kalakand).

FDT-214 · What is the difference between condensed milk and evaporated milk?

Both are concentrated milk. Sweetened condensed milk has added sucrose, which lowers aw and preserves it without sterilization. Evaporated milk is unsweetened and must be sterilised in the can.

FDT-215 · How is lactose-free milk produced?

The enzyme lactase (β-galactosidase) hydrolyses lactose into glucose and galactose. Alternatively, lactose is removed by membrane filtration and the remainder hydrolysed. The product tastes sweeter without added sugar.

Cereal, Bakery & Confectionery

FDT-216 · What is the extraction rate in wheat milling?

The percentage of flour obtained from cleaned wheat. White flour (maida) is about 70–75%, and whole-wheat atta approaches 95–100%. Higher extraction gives more bran, fibre, minerals and ash, and a darker colour.

FDT-217 · What is the falling number test?

A measure of α-amylase activity. A flour–water slurry is gelatinised in a boiling bath, and the time for a plunger to fall is recorded. A low falling number means high enzyme activity, often from sprouted grain, and gives a sticky crumb.

FDT-218 · What does a farinograph measure?

Dough resistance to mixing at constant consistency (500 BU). It gives water absorption, dough development time, stability and mixing tolerance, which indicate flour strength for bread or biscuits.

FDT-219 · What are the main bread-making methods?

The straight dough method (all ingredients mixed at once), the sponge-and-dough method (pre-ferment then dough), and the Chorleywood Bread Process, which uses high-energy mechanical development to cut bulk fermentation time.

FDT-220 · What happens during baking of bread?

Oven spring as gas expands and yeast activity peaks. Then yeast dies (about 55–60 °C), starch gelatinises, gluten coagulates (about 70–80 °C), the crust dries and browns by Maillard reaction and caramelization, and the crumb sets.

FDT-221 · What are dough improvers?

Additives that strengthen dough and improve loaf volume and texture, such as ascorbic acid (an oxidant), enzymes (amylases, xylanases), emulsifiers (DATEM, SSL) and vital gluten.

FDT-222 · What is the difference between hard dough and soft dough biscuits?

Hard dough (e.g. Marie, crackers) has low sugar and fat, a developed gluten network and is sheeted and docked. Soft dough (e.g. cookies, shortbread) is high in sugar and fat with little gluten development and is rotary-moulded or wire-cut.

FDT-223 · What are the benefits of parboiling rice?

Higher head-rice yield (less breakage), thiamine and other nutrients migrating inward, lower losses on milling and washing, better resistance to insects and stable bran oil. The drawbacks are colour change, longer cooking time and energy use.

FDT-224 · What is conching in chocolate making?

Prolonged mixing and aeration of chocolate mass at elevated temperature. It drives off volatile acids and moisture, coats particles with cocoa butter, reduces viscosity and develops smooth texture and flavour.

FDT-225 · What is chocolate bloom?

A whitish surface. Fat bloom comes from cocoa butter migrating and recrystallising into Form VI, due to poor tempering, temperature cycling or fat migration. Sugar bloom forms when surface moisture dissolves sugar that recrystallises.

FDT-226 · What are the sugar-boiling stages in confectionery?

As temperature rises: thread (about 110 °C), soft ball (about 112–116 °C, fudge), firm ball (about 118–120 °C), hard ball (about 121–130 °C), soft crack (about 132–143 °C, toffee), hard crack (about 146–154 °C, hard candy) and caramel (above about 160 °C).

FDT-227 · Why is glucose syrup used in sugar confectionery?

It acts as a "doctor" that inhibits sucrose crystallisation, controls sweetness, viscosity and hygroscopicity, and helps form an amorphous glass in hard candies.

FDT-228 · What is resistant starch?

Starch that escapes digestion in the small intestine and is fermented in the colon. Types are RS1 (physically inaccessible), RS2 (raw granules, e.g. green banana), RS3 (retrograded), RS4 (chemically modified) and RS5 (amylose–lipid complexes).

Fruit & Vegetable Processing

FDT-229 · How do sugar, acid and pectin interact to set a high-methoxyl pectin gel?

Sugar dehydrates pectin chains, and acid at pH about 2.8–3.4 suppresses carboxyl ionisation so that chains associate by hydrogen bonding and hydrophobic interactions. Gelling needs about 0.5–1% pectin and at least 55–65% soluble solids.

FDT-230 · How is enzymatic browning prevented during fruit processing?

By blanching to inactivate polyphenol oxidase, dipping in ascorbic acid, citric acid or calcium ascorbate, using sulphites where permitted, excluding oxygen with syrup, vacuum or MAP, and chilling.

FDT-231 · How is fruit juice clarified?

Pectinase and amylase are added to break down haze-forming colloids. Fining agents (gelatin, bentonite, silica sol) are then used, followed by filtration or ultrafiltration and centrifugation.

FDT-232 · How are fruit juice concentrates produced?

Juice is concentrated in multi-effect or falling-film vacuum evaporators to about 65–70 °Brix, with volatile aroma recovery and add-back. Freeze concentration and reverse osmosis are gentler alternatives.

FDT-233 · Why is blanching required before freezing vegetables but not most fruits?

Vegetables contain enzymes such as lipoxygenase and peroxidase that cause off-flavours and colour loss during frozen storage. Blanching would damage the delicate texture of fruits, so they are protected instead with sugar syrup or ascorbic acid.

FDT-234 · What enzymes are used as blanching adequacy indicators?

Peroxidase, because it is among the most heat-stable enzymes in vegetables. Its inactivation implies other enzymes are inactivated. Catalase is sometimes used, and lipoxygenase is more relevant to quality in some vegetables.

FDT-235 · What is osmotic dehydration of fruits?

Partially removing water by immersing fruit pieces in concentrated sugar or salt solutions. Water flows out while some solute enters. It is often followed by air drying to produce intermediate-moisture fruits with better colour and flavour.

FDT-236 · What are the steps in tomato paste processing?

Washing, sorting, crushing, then hot break (about 85–95 °C, which inactivates pectic enzymes for viscosity) or cold break (about 65–70 °C, for colour and flavour). This is followed by pulping and finishing, vacuum evaporation to about 28–30 °Brix, and aseptic filling or hot filling.

FDT-237 · What is the principle of sulphuring dried fruits?

Exposing fruits to SO₂ gas or dipping them in sulphite solutions. SO₂ inhibits enzymatic and non-enzymatic browning, acts as an antimicrobial and protects vitamin C and carotenoids. Residues are regulated because sulphites can trigger asthma in sensitive people.

FDT-238 · How does 1-MCP extend the shelf life of fruits?

1-Methylcyclopropene binds irreversibly to ethylene receptors and blocks ethylene action, so it delays ripening, softening and senescence in climacteric fruits such as apples and bananas.

FDT-239 · What is minimal processing of fruits and vegetables?

Fresh-cut processing (washing, peeling, cutting, sanitising, packaging under MAP and chilling) that keeps produce fresh-like and convenient. Cut tissue respires faster and is more vulnerable to microbes and browning.

FDT-240 · What is pre-cooling of produce, and which methods are used?

Rapidly removing field heat after harvest to slow respiration and decay. Methods include room cooling, forced-air cooling, hydrocooling, vacuum cooling (for leafy greens) and package icing.

Meat, Fish & Poultry

FDT-241 · What are PSE and DFD meat?

PSE (pale, soft, exudative) results when pH falls rapidly while the carcass is still hot, often in stress-susceptible pigs, and denatures proteins. DFD (dark, firm, dry) results when glycogen was depleted by pre-slaughter stress, leaving ultimate pH high (above about 6.0), which favours spoilage.

FDT-242 · How does post-mortem pH change in muscle?

Anaerobic glycolysis converts glycogen to lactic acid, so pH falls from about 7.0 in live muscle to an ultimate pH of about 5.4–5.8 in normal meat within about 24 hours.

FDT-243 · What is cold shortening?

Severe contraction of pre-rigor muscle chilled below about 10–15 °C while ATP is still present, which makes the meat tough. It is prevented by electrical stimulation, controlled chilling or hanging carcasses by the pelvis.

FDT-244 · What causes the pink colour of cured meat?

Nitrite forms nitric oxide, which binds myoglobin to form nitrosylmyoglobin (red). On cooking this becomes nitrosyl hemochrome, the stable pink colour of ham and bacon.

FDT-245 · What are TMA and TVB-N in fish quality?

Bacteria reduce trimethylamine oxide to trimethylamine (TMA), which gives the "fishy" odour. Total volatile basic nitrogen (TVB-N) includes TMA, ammonia and dimethylamine. Both rise with spoilage and are used as freshness indices.

FDT-246 · What is scombroid (histamine) poisoning?

An illness caused by histamine formed when bacteria decarboxylate histidine in temperature-abused fish such as tuna, mackerel and sardines. Histamine is heat-stable, so cooking does not prevent it. Rapid chilling is the control.

FDT-247 · What are safe internal cooking temperatures for meats?

Commonly cited (USDA) values: poultry 74 °C (165 °F); ground beef and pork 71 °C (160 °F); whole cuts of beef, pork and lamb 63 °C (145 °F) with a 3-minute rest. Doneness should be checked with a thermometer, not by colour.

FDT-248 · How is the water-holding capacity of meat affected by pH?

WHC is lowest near the isoelectric point of myofibrillar proteins (about pH 5.0–5.2), where net charge and electrostatic repulsion are minimal. Raising pH (e.g. with phosphates) or adding salt increases WHC and yield.

FDT-249 · What is the role of phosphates in processed meat?

They raise pH and ionic strength, dissociate actomyosin and chelate metals. This increases water binding, protein extraction, emulsion stability and yield, and reduces oxidation.

FDT-250 · What is a meat emulsion?

A fine comminuted system, as in frankfurters, in which fat particles are coated by salt-solubilised myofibrillar proteins in a continuous aqueous matrix. Chopping temperature must stay below about 12–15 °C to avoid emulsion breakdown.

FDT-251 · How are poultry carcasses processed in a plant?

Stunning, bleeding, scalding (about 50–60 °C), defeathering, evisceration, inspection, washing, chilling (immersion or air, to below about 4 °C), grading and packaging.

FDT-252 · How is fish freshness assessed by sensory means?

By bright, convex eyes; bright red gills; firm, elastic flesh; shiny skin with clear mucus; and a fresh seaweedy odour. Schemes such as the Quality Index Method (QIM) score these attributes.

Food Packaging

FDT-253 · What is modified atmosphere packaging (MAP) and which gases are used?

Replacing the air in a pack with a tailored gas mix. CO₂ inhibits bacteria and moulds, N₂ is an inert filler that prevents collapse, and O₂ is used at high levels for red-meat colour or at low levels to avoid anaerobiosis in produce.

FDT-254 · What is the difference between MAP and CAP?

MAP sets the atmosphere once at sealing, after which it changes passively with respiration and permeation. Controlled atmosphere packaging or storage continuously monitors and adjusts gas composition.

FDT-255 · What is equilibrium modified atmosphere packaging (EMAP)?

Packaging for fresh produce in which film permeability is matched to the produce's respiration rate. O₂ falls and CO₂ rises to a steady beneficial level, typically a few percent each.

FDT-256 · What is migration from food packaging?

Transfer of substances such as monomers, plasticisers, additives, inks and adhesives from packaging into food. Overall migration is the total transferred; specific migration covers individual substances. Both are tested with food simulants.

FDT-257 · What is the purpose of multilayer laminates?

To combine the properties of several materials: PET for strength and printability, aluminium foil or EVOH for gas barrier, PE or PP for sealability and moisture barrier, and adhesive tie layers between them.

FDT-258 · How does humidity affect EVOH barrier properties?

EVOH is an excellent oxygen barrier when dry, but its OTR rises sharply at high relative humidity because water plasticises it. It is therefore buried between moisture-barrier layers such as PP or PE.

FDT-259 · What is a double seam in a can?

The hermetic joint formed by interlocking the can body flange and end curl in two rolling operations, with sealing compound. Key measurements are seam thickness, width, countersink, body hook, cover hook and overlap.

FDT-260 · What are oxygen scavengers and how do they work?

Active components, often iron powder in sachets or polymer-based scavengers in films and closures, that react with residual oxygen to bring headspace O₂ below about 0.01%. This protects against oxidation and mould.

FDT-261 · What are time–temperature indicators (TTIs)?

Labels that show cumulative time–temperature exposure through irreversible colour change, based on enzymatic, polymerisation or diffusion reactions. They are used to monitor the cold chain for chilled or frozen foods and vaccines.

FDT-262 · What are biodegradable and compostable packaging materials?

Materials broken down by microbes, such as PLA, PHA, starch blends and cellulose films. "Compostable" means they break down under specified composting conditions within a set time. Industrial composting is often required.

FDT-263 · What is the difference between rigid, semi-rigid and flexible packaging?

Rigid packaging keeps its shape (glass, metal cans, thick plastic bottles). Semi-rigid packaging deforms but recovers (thermoformed trays, cartons). Flexible packaging takes the shape of its contents (films, pouches, foil).

FDT-264 · Why is aluminium preferred for beverage cans?

It is lightweight, corrosion-resistant with internal lacquer, easily formed into two-piece drawn-and-ironed cans, a complete light and gas barrier, quick to chill and highly recyclable.

Food Engineering Unit Operations

FDT-265 · What are the constant-rate and falling-rate periods in drying?

In the constant-rate period, the surface stays saturated and evaporation proceeds at wet-bulb temperature, controlled by external heat and mass transfer. Below the critical moisture content, internal diffusion controls the rate and it falls progressively.

FDT-266 · What is steam economy in evaporators?

Mass of water evaporated per mass of steam supplied. A single effect gives about 0.8–1. Multiple-effect evaporators reuse vapour as heating medium, so economy approaches n per n effects (slightly less). Thermal or mechanical vapour recompression raises it further.

FDT-267 · Why are falling-film evaporators widely used in the dairy and juice industries?

They have very short residence time, low temperature difference and high heat-transfer coefficients. This makes them suitable for heat-sensitive liquids under vacuum and easy to stage as multiple effects.

FDT-268 · What is the difference between shear-thinning, shear-thickening and Bingham plastic fluids?

Shear-thinning (pseudoplastic) fluids lose viscosity as shear rate rises, e.g. sauces and juice concentrates. Shear-thickening (dilatant) fluids gain viscosity, e.g. concentrated starch slurry. Bingham plastic fluids need a yield stress before flowing, e.g. tomato ketchup and chocolate.

FDT-269 · What is the power-law model for food fluids?

τ = K·γ̇ⁿ, where K is the consistency coefficient (Pa·sⁿ) and n is the flow behaviour index. n < 1 is shear-thinning, n = 1 Newtonian and n > 1 shear-thickening. Herschel–Bulkley adds a yield stress: τ = τ₀ + K·γ̇ⁿ.

FDT-270 · State Stokes' law and its relevance to cream separation.

Settling velocity v = d²(ρp − ρf)g ÷ (18μ). It shows that separation speed rises with the square of particle diameter and with density difference. Centrifuges replace g with ω²r to accelerate the separation of fat globules.

FDT-271 · What are Rittinger's, Kick's and Bond's laws?

Energy laws for size reduction. Rittinger: E ∝ (1/x₂ − 1/x₁), for fine grinding. Kick: E ∝ ln(x₁/x₂), for coarse crushing. Bond: E = 10·Wi·(1/√P − 1/√F), with sizes in µm and Wi the work index in kWh/t, for intermediate sizes.

FDT-272 · How does a two-stage homogeniser work?

In the first stage, at high pressure (often about 10–25 MPa for milk), fat globules are disrupted by turbulence, cavitation and shear in the valve gap. The second stage, at lower pressure (about 3–5 MPa), breaks up fat-globule clusters.

FDT-273 · What is the Reynolds number and why does it matter in food processing?

Re = ρvD/μ, the ratio of inertial to viscous forces. Re < 2100 is laminar and Re > about 4000 turbulent in pipes. It affects heat transfer, residence-time distribution in holding tubes and CIP effectiveness.

FDT-274 · What is the regeneration section of an HTST pasteurizer?

A heat exchanger section where hot pasteurised milk preheats incoming cold raw milk while being cooled itself. It typically recovers about 85–95% of the heat. Pasteurised milk is kept at higher pressure than raw milk to avoid contamination through leaks.

FDT-275 · What are the drying methods for foods, and how are they chosen?

Tray or cabinet, tunnel, belt, fluidised-bed, drum, spray, vacuum and freeze drying. The choice depends on feed form (liquid, paste, particulate), heat sensitivity, required quality, throughput and cost.

FDT-276 · What is Plank's equation for freezing time?

t = (ρL/(Tf − Ta))·(P·a/h + R·a²/k), where a is thickness or diameter, h the surface heat-transfer coefficient, k the thermal conductivity of frozen food, and P, R are shape factors (slab 1/2, 1/8; cylinder 1/4, 1/16; sphere 1/6, 1/24).

Food Safety & Quality Systems

FDT-277 · What are the 7 principles of HACCP?

• Conduct a hazard analysis. 2. Determine CCPs. 3. Establish critical limits. 4. Establish monitoring procedures. 5. Establish corrective actions. 6. Establish verification procedures. 7. Establish documentation and record-keeping.

FDT-278 · What are the 5 preliminary steps of HACCP?

Assemble the HACCP team, describe the product, identify intended use and consumers, construct a flow diagram and verify the flow diagram on-site. With the 7 principles, these make the Codex 12 steps.

FDT-279 · How is a CCP decision tree used?

It is a sequence of yes/no questions applied to each hazard at each step: whether control measures exist, whether the step eliminates or reduces the hazard, whether contamination could exceed limits and whether a later step will control it. This determines whether the step is a CCP.

FDT-280 · What is the difference between a critical limit and an operational limit?

A critical limit is the value separating acceptable from unacceptable at a CCP, e.g. 72 °C for 15 s. An operational limit is a tighter target, e.g. 73.5 °C, at which operators adjust the process before the critical limit is breached.

FDT-281 · What is an OPRP in ISO 22000?

An operational prerequisite programme: a control measure or combination applied to prevent or reduce a significant food-safety hazard to an acceptable level, managed with action criteria and monitoring. It is not a CCP with measurable critical limits.

FDT-282 · What is the difference between verification and validation in HACCP?

Validation obtains evidence before implementation that control measures can effectively control the hazard, e.g. challenge studies. Verification confirms on an ongoing basis that the plan is being followed and works, e.g. record review, audits and testing.

FDT-283 · What is FSSC 22000?

A GFSI-recognised certification scheme that combines ISO 22000 with sector-specific prerequisite programme standards (e.g. ISO/TS 22002-1 for food manufacturing) and additional scheme requirements.

FDT-284 · What is GFSI?

The Global Food Safety Initiative, an industry-led body that benchmarks food-safety certification programmes such as FSSC 22000, BRCGS, SQF and IFS, so that one audit is widely accepted by retailers.

FDT-285 · What are TACCP and VACCP?

TACCP (Threat Assessment CCP) addresses deliberate, often ideologically motivated, tampering and food defence. VACCP (Vulnerability Assessment CCP) addresses economically motivated adulteration, i.e. food fraud.

FDT-286 · What is the triangle test in sensory evaluation?

A discrimination test in which panellists receive three coded samples, two identical and one different, and identify the odd one. The chance probability is 1/3, and significance is judged from binomial tables.

FDT-287 · How are CIP cycles typically sequenced?

Pre-rinse with water, then hot alkaline wash (e.g. NaOH about 0.5–2% at about 70–80 °C) to remove protein and fat, intermediate rinse, acid wash (e.g. nitric or phosphoric) to remove mineral scale, final rinse, and sanitisation.

FDT-288 · What is environmental monitoring in food plants?

Systematic swabbing of food-contact surfaces, non-contact surfaces, drains and air by zones (Zone 1 to 4) to detect pathogens such as *Listeria* or indicator organisms, so that harbourage sites are found before product contamination.

Food Regulations & Nutrition

FDT-289 · What is FSSAI and what are its main functions?

The Food Safety and Standards Authority of India, a statutory body under the Ministry of Health and Family Welfare, established under the FSS Act, 2006. It frames food standards and regulations, licenses and registers food businesses, accredits laboratories, oversees imports, enforces through state authorities and runs consumer initiatives such as Eat Right India.

FDT-290 · What are the mandatory label declarations under FSSAI labelling regulations?

Name of food, list of ingredients in descending order of weight, nutritional information, veg or non-veg logo, food additives declaration, manufacturer's name and address, FSSAI licence or registration number, net quantity, lot or batch number, date marking, country of origin for imports and instructions for use where needed.

FDT-291 · What is FSMA?

The US Food Safety Modernization Act, 2011. It shifted the FDA's focus from responding to contamination to preventing it, with rules on preventive controls (HARPC), produce safety, the Foreign Supplier Verification Programme, sanitary transport and intentional adulteration.

FDT-292 · What is GRAS?

"Generally Recognized as Safe": a US FDA designation for substances considered safe by qualified experts for their intended use, based on scientific data or a history of common use, which are exempt from food-additive premarket approval.

FDT-293 · What is ADI?

Acceptable Daily Intake: the amount of an additive or residue, in mg/kg body weight per day, that can be consumed daily over a lifetime without appreciable health risk. It is usually derived from the NOAEL divided by a 100-fold safety factor.

FDT-294 · What is MRL?

Maximum Residue Limit: the highest legally permitted concentration of a pesticide or veterinary drug residue in a food, based on good agricultural practice and dietary risk assessment.

FDT-295 · What is the glycemic index (GI)?

The blood-glucose response to a food with 50 g available carbohydrate, relative to glucose (= 100). GI ≤ 55 is low, 56–69 medium and ≥ 70 high. Glycemic load = GI × carbohydrate per serving ÷ 100.

FDT-296 · What are PDCAAS and DIAAS?

Protein quality scores. PDCAAS = limiting amino acid score × faecal protein digestibility, truncated at 1.0. DIAAS, recommended by FAO in 2013, uses ileal digestibility of each indispensable amino acid and is not truncated.

FDT-297 · What are nutrition and health claims?

Nutrition claims describe nutrient content or comparisons, e.g. "low fat" or "high fibre". Health claims link a food or constituent to health, e.g. "calcium helps build strong bones". Codex and FSSAI permit them only when specified conditions are met and substantiated.

FDT-298 · What is the difference between food additives and processing aids?

Additives are intentionally added for a technological function and remain in the final food, so they are labelled (e.g. colours, preservatives). Processing aids are used during processing and are absent or present only as unintended residues (e.g. clarifying agents, some enzymes).

FDT-299 · What are nutraceuticals and functional foods under FSSAI?

FSSAI regulates health supplements, nutraceuticals, foods for special dietary use, foods for special medical purposes, specialty foods with plant or botanical ingredients and probiotic and prebiotic foods under dedicated regulations. They must use permitted ingredients and dose limits and carry required label warnings.

FDT-300 · What is the Eat Right India movement?

An FSSAI initiative promoting safe, healthy and sustainable diets through measures such as reducing salt, sugar and trans fat, fortification (+F), hygiene ratings, Eat Right campuses, clean street-food hubs and consumer awareness.

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