Scope & History of Microbiology

• Composition and Definition of Ghee:
• Clarified Butter Fat (Ghee):
• Manufactured by thermal clarification of butter or cream at $110 - 120^\circ\text{C}$ to evaporate moisture ($\lt 0.5\%$) and remove browned milk curd residue.
• Contains $\ge 99.5\%$ pure anhydrous milk fat, exhibiting granular texture and pleasant carmelized lactone/diacetyl aroma.
• Conclusion: Ghee (Option 3).

Correct option: (3) Ghee

• Microbial Load Comparison in Dairy Commodities:
• Raw Milk:
• Fresh, unprocessed bovine milk directly from farm milking contains endogenous udder microflora, teat canal contaminants, and environmental dust/manure bacteria, easily yielding total viable counts of $10^5 - 10^7\text{ CFU/mL}$.
• In contrast, Skim milk powder, Sweetened condensed milk, and Butter undergo pasteurization, thermal evaporation, and water-activity suppression, resulting in drastically lower microbial counts.
• Conclusion: Raw Milk (Option 4).

Correct option: (4) Raw Milk

• Succession of Microbial Flora in Stored Raw Milk at Ambient Conditions:
• Sequential Ecological Phases:

• Bactericidal / Germicidal stage: Fresh milk resists bacterial growth due to natural indigenous inhibitors (lactoperoxidase system, lysozyme, lactoferrin).
• Development of mixed microflora: Heterogeneous acid-producing streptococci and saprophytes multiply as native inhibitors diminish.
• Growth of lactic acid bacteria: Lactococci and Lactobacilli dominate, fermenting lactose into lactic acid and depressing pH ($\lt 4.5$), coagulating casein.
• Growth of yeasts and molds: Acid-tolerant yeasts and molds (Geotrichum, Candida) utilize accumulated lactic acid, deacidifying the medium.
• Decomposing bacterial flora: Proteolytic and putrefactive bacteria (Pseudomonas, Bacillus) degrade proteins and lipids, causing spoilage.
  • Correct Sequence: (D) $\rightarrow$ (E) $\rightarrow$ (A) $\rightarrow$ (B) $\rightarrow$ (C).

• Conclusion: (D), (E), (A), (B) and (C) (Option 4).

• Deteriorative Mechanisms in Skim Milk Powder (SMP):
• Maillard Browning Reaction:
• SMP contains approximately $50\%$ lactose (reducing carbohydrate) and $36\%$ protein (rich in free $\epsilon$-amino groups of lysine), with negligible fat ($\lt 1.5\%$).
• During storage—especially under elevated ambient temperature or moisture ($a_w \gt 0.2$)—non-enzymatic Maillard browning proceeds rapidly between reducing sugars and amino acid residues.
• Results in brown melanoidin pigments, stale/cereal off-flavors, insolubility, and loss of essential lysine bioavailability.
• Conclusion: Maillard browning (Option 4).

Correct option: (4) Maillard browning