Starter Cultures & Fermented Products

Key historical landmarks in dairy bacteriology:

• Introduction of starter cultures in 1905 in England was initiated by J. Stubbs: (A)-(II).
• First application of pure starter cultures for developing aroma and flavor in butter was demonstrated in 1890 independently by V. Storch (Denmark) and H. W. Conn (USA): (B)-(III).
• Christian Hansen Laboratory (Denmark) introduced commercial starter cultures for cheese and butter making for the first time in the late 19th century: (C)-(IV).
• Joseph Lister discovered and isolated the first pure culture of a bacterium, Bacterium lactis (Lactococcus lactis), using serial dilution in 1878: (D)-(I).
  
  Option analysis:
• (II), (B)-(III), (C)-(IV), (D)-(I): Correct matching.
• (I), (B)-(II), (C)-(III), (D)-(IV): Incorrect.
• (III), (B)-(II), (C)-(IV), (D)-(I): Incorrect.
• (IV), (B)-(III), (C)-(I), (D)-(II): Incorrect.

Lactobacilli are grouped into three physiological fermentation classes:

• Obligately homofermentative (Group I): Ferment hexoses exclusively to lactic acid via EMP pathway, unable to ferment pentoses (e.g. Lactobacillus helveticus, Lactobacillus acidophilus, Lactobacillus delbrueckii).
• Facultatively heterofermentative (Group II): Ferment hexoses to lactic acid via EMP pathway, but also possess phosphoketolase to ferment pentoses into lactic acid and acetic acid (e.g. Lacticaseibacillus casei, Lacticaseibacillus paracasei, Lactiplantibacillus plantarum).
• Obligately heterofermentative (Group III): Ferment hexoses and pentoses via the phosphoketolase pathway producing lactic acid, ethanol/acetic acid, and $CO_2$ (e.g. Limosilactobacillus fermentum, Levilactobacillus brevis).
  
  Option analysis:
• Lactobacillus helveticus: Obligately homofermentative.
• Limosilactobacillus fermentum: Obligately heterofermentative.
• Levilactobacillus brevis: Obligately heterofermentative.
• Lacticaseibacillus casei: Correct. A facultatively heterofermentative lactic acid bacterium.

Characteristics of dairy starter cultures:

• Statement (I) is false: Defined multiple-strain starter cultures consist of a known number of distinct, well-characterized pure strains blended together in known, predetermined proportions (it is mixed-strain cultures, not defined multiple-strain cultures, that contain organisms in unknown, undefined proportions).
• Statement (II) is false: Single-strain starter cultures are extremely vulnerable to complete failure if a single homologous phage attacks that specific strain. In contrast, multiple-strain cultures provide insurance against phage attack because even if one strain is lysed by phage, the other insensitive strains continue to produce acid. Thus, multiple-strain cultures are LESS prone to failure from phage attack than single-strain cultures.
  
  Option analysis:
• Both Statement (I) and Statement (II) are true: Incorrect.
• Both Statement (I) and Statement (II) are false: Correct.
• Statement (I) is true but Statement (II) is false: Incorrect.
• Statement (I) is false but Statement (II) is true: Incorrect.

Correct matching is:

• Pseudomonas $\rightarrow$ (III) Spoilage (psychrotrophic production of heat-stable lipases and proteases causing bitter, fruity, or rancid defects).
• S. thermophilus, L. lactis ssp. lactis $\rightarrow$ (IV) Acid Production (ferments lactose to lactic acid).
• Enterobacteriaceae $\rightarrow$ (I) Pathogenic and spoilage both (includes pathogenic Salmonella/E. coli as well as coliforms that cause gas and off-flavors).
• L. lactis subsp. lactis bv. diacetylactis $\rightarrow$ (II) Flavour production (ferments citrate to diacetyl, giving characteristic buttery aroma).