(a) Describe the processing of yoghurt and cultured buttermilk along with flow diagrams. (20 marks) (b) Discuss the role of the…

(a) Processing of yoghurt and cultured buttermilk, with flow diagrams (20 marks)

Both are made by lactic fermentation of heat-treated milk with a defined starter, but they differ in milk composition, culture and temperature.

Yoghurt. Milk is standardised to 3 to 3.5% fat and 14 to 15% solids-not-fat, with added skim milk powder if needed, to give a firm body. It is homogenised at about 60 °C and 150 to 200 bar to prevent creaming, then heated at 85 to 90 °C for 15 to 30 minutes, which kills competing organisms and denatures whey proteins so that the gel is firm. It is cooled to 42 to 45 °C and inoculated with 2 to 3% of a 1:1 mixed culture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, which grow together (protocooperation). Incubation for 3 to 4 hours gives a pH of 4.5 to 4.6 and about 0.9% lactic acid, with acetaldehyde as the typical flavour. In set yoghurt this is done in the retail pack; in stirred yoghurt it is done in a tank, and the coagulum is broken, cooled to 4 to 5 °C, mixed with fruit or flavour and packed. Storage is at 4 °C.

Cultured buttermilk. Skim or low-fat milk (0.5 to 1% fat) is heated at 85 to 90 °C for 30 minutes, cooled to 20 to 22 °C and inoculated with about 1% of a mesophilic culture of Lactococcus lactis subsp. lactis and cremoris, with L. lactis subsp. lactis biovar diacetylactis and Leuconostoc species that ferment citrate to diacetyl for the buttery flavour. It is held for 12 to 16 hours to about pH 4.5 (0.8 to 0.9% acidity). The curd is broken by gentle stirring, cooled to about 5 °C, salted at 0.1 to 0.2% and flavoured if desired, then packed and stored at 4 to 5 °C.

(b) Role of the WTO in implementing sanitary and phytosanitary measures for milk and meat products (15 marks)

The WTO Agreement on the Application of Sanitary and Phytosanitary (SPS) Measures, in force since 1995, lets members protect human, animal and plant life and health, but stops such measures from becoming disguised trade barriers. Its role for milk and meat trade is as follows:

• Scientific basis: measures must rest on scientific evidence and a risk assessment, be applied only to the extent necessary, and not discriminate between members in similar conditions.
• Harmonisation: members are encouraged to base measures on the standards of the three bodies named in the Agreement, Codex Alimentarius (food safety, including residue limits and hygiene codes for milk and meat), the World Organisation for Animal Health (animal diseases such as foot-and-mouth disease, BSE and avian influenza) and the International Plant Protection Convention (plant pests, relevant to imported feed grains and fodder).
• Equivalence and regionalisation: an importer should accept different measures that give the same protection, and recognise disease-free areas or zones.
• Transparency: notification of new measures and national enquiry points.
• SPS Committee: a forum in which members raise specific trade concerns, such as import bans over residues or disease status, with the dispute settlement system as the last resort.
• Technical assistance to developing countries, including through the Standards and Trade Development Facility.

For India, this means aligning milk and meat exports with Codex and WOAH standards, residue monitoring, disease-free zones, HACCP and certification by the Export Inspection Council and FSSAI.

(c) Curing ingredients in meat processing, with advantages and limitations of curing methods (15 marks)

Functions of curing ingredients:

• Common salt (about 2 to 3%): preserves by lowering water activity, adds flavour, and solubilises myofibrillar proteins so that water and fat are bound.
• Nitrite (and nitrate, which bacteria reduce to nitrite): forms nitric oxide, which combines with myoglobin to give the stable pink nitrosohaemochrome, contributes cured flavour, inhibits Clostridium botulinum and delays rancidity. Its level is legally limited because of nitrosamine formation.
• Sugar: offsets the harshness of salt, adds flavour and feeds lactic bacteria in fermented products.
• Ascorbate or erythorbate (cure accelerators): speed up the reduction of nitrite to nitric oxide and reduce nitrosamine formation.
• Phosphates (about 0.3 to 0.5%): raise pH and water-holding capacity and improve yield.
• Spices and smoke: flavour, and antioxidant and antimicrobial action.

Curing methods:

• Dry curing (rubbing the mixture on the surface). Advantages: simple, long shelf life, intense flavour. Limitations: slow and uneven, high salt, 20 to 30% weight loss.
• Wet (brine) curing by immersion. Advantages: uniform, less shrinkage. Limitations: slow for thick cuts, bulky, needs refrigeration, and the brine can spoil.
• Injection (pumping) with brine, often with tumbling. Advantages: fast (hours), uniform, high yield. Limitations: equipment cost, contamination along needle tracks, less traditional flavour.
• Direct addition of the cure to comminuted meat: quick and uniform, but needs accurate dosing.