applications of microbiology in food production

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Questions and Answers

Which of the following best describes the role of heating milk to approximately 85°C in yogurt production?

  • It ensures the lactose is completely broken down before bacterial culture is added.
  • It inhibits the growth of any unwanted bacteria before fermentation.
  • It denatures milk proteins, allowing them to set together for a smoother texture. (correct)
  • It neutralizes any existing lactic acid, preventing premature coagulation.

What is the primary function of lactic acid produced during yogurt fermentation?

  • To act on milk protein (casein), giving yogurt its characteristic texture and tang. (correct)
  • To break down fats into simpler compounds, enhancing digestibility.
  • To neutralize any harmful bacteria present in the raw milk.
  • To convert complex sugars into simpler, sweeter compounds.

In cheese production, what is the purpose of adding starter bacteria to milk?

  • To introduce specific molds that contribute to the cheese's unique flavour profile.
  • To increase the protein content of the cheese, resulting in a firmer texture.
  • To convert milk sugars into lactic acid, aiding in coagulation and flavour development. (correct)
  • To neutralize any remaining enzymes in the milk, preventing spoilage.

Which of the following factors has the LEAST impact on the style, texture, and flavour of cheese?

<p>The ambient temperature during cheese consumption. (C)</p> Signup and view all the answers

Which of the following is NOT a typical method of curdling milk in cheese production?

<p>Boiling at extremely high temperatures. (B)</p> Signup and view all the answers

Why is nonfat dry milk (NFDM) or scalded milk sometimes used in yogurt production?

<p>To increase milk thickness, as heating denatures whey proteins. (A)</p> Signup and view all the answers

What is the role of Kappa-casein and Beta-lactoglobulin in yogurt production, and how is it affected by heating the milk?

<p>They are key proteins, and heating changes their interactions so that short, branched micelle chains form incorporating whey. (D)</p> Signup and view all the answers

A yogurt manufacturer wants to reduce the fermentation time of their yogurt. Which adjustment to their process would MOST likely achieve this goal?

<p>Increasing incubation temperature to encourage bacterial activity, but without denaturing the bacterial culture. (A)</p> Signup and view all the answers

Why is Propionibacter shermani important in the production of Swiss cheese?

<p>It generates carbon dioxide, forming the characteristic 'eyes' in the cheese. (C)</p> Signup and view all the answers

What is the primary purpose of heating the curd during the production of some hard cheeses?

<p>To expel more whey from the curd. (D)</p> Signup and view all the answers

What key role does salt play in cheese production, beyond just adding flavor?

<p>It draws moisture from the curd and firms the cheese's texture. (C)</p> Signup and view all the answers

How does 'cheddaring' contribute to the unique characteristics of cheddar cheese?

<p>It helps remove moisture and influences the final texture. (C)</p> Signup and view all the answers

What is the main purpose of washing the curd in warm water during the production of cheeses like Edam and Gouda?

<p>To lower the acidity and produce a milder flavor. (D)</p> Signup and view all the answers

What is the key transformation that occurs during the ripening stage of cheese production?

<p>The breakdown of proteins and fats by microbes and enzymes. (C)</p> Signup and view all the answers

Which of the following describes the function of Penicillium molds in the ripening of soft cheeses like Brie and Camembert?

<p>They form a white crust on the exterior, contributing to texture and flavor. (D)</p> Signup and view all the answers

How do the molds used in blue cheese production, such as Penicillium roqueforti, contribute to the cheese's characteristics?

<p>They form distinct blue veins and often assertive flavors. (A)</p> Signup and view all the answers

What proteolytic enzymes are added to cheese but not yogurt, and what is their function?

<p>Rennet; to promote protein coagulation (A)</p> Signup and view all the answers

How does the fermentation process using Saccharomyces cerevisiae contribute to the texture of bread?

<p>It yields carbon dioxide, creating a porous and light texture. (D)</p> Signup and view all the answers

What is the primary function of Acetobacter aceti in vinegar production?

<p>It oxidizes alcohol to acetic acid. (C)</p> Signup and view all the answers

In pickle fermentation, what roles do Leuconostoc mesenteroides and Pediococcus species play concerning salt concentration?

<p><em>L. mesenteroides</em> dominates in low-salt brines, while <em>Pediococcus</em> is more active in high-salt. (B)</p> Signup and view all the answers

How does Aspergillus oryzae contribute to the production of soy sauce?

<p>It breaks down starch into fermentable glucose. (D)</p> Signup and view all the answers

What is 'Moromi' in the context of soy sauce production?

<p>The mash of koji mixed with salt water for fermentation. (B)</p> Signup and view all the answers

What role do Pediococcus soyae and Saccharomyces rouxii play in the soy sauce fermentation process?

<p>They break down protein residues into amino acids and peptides. (B)</p> Signup and view all the answers

Flashcards

Yogurt

A food made from bacterial fermentation of milk.

Yogurt cultures

Bacteria used to ferment milk into yogurt, primarily Lactobacillus and Streptococcus species.

Fermentation

The process where bacteria convert lactose into lactic acid, affecting milk texture.

Lactic acid

An acid produced by bacteria during the fermentation of lactose in yogurt.

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Coagulation

The curdling of milk proteins into solid curds through acid and bacteria.

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Rennet

An enzyme used to help curdle milk in cheese production.

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Incubation temperature for yogurt

The optimal temperature (40-46 °C) for fermenting yogurt.

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Cheese production

Creating cheese through curdling milk and separating curds from whey.

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Propionibacter shermani

A bacterium that generates carbon dioxide during cheese aging, forming holes in Swiss cheese.

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Curd processing

The step where cheese curds are cut, heated, and manipulated to remove whey and shape cheese.

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Thermophilic bacteria

Heat-loving bacteria like Lactobacilli that influence cheese flavor and texture during processing.

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Role of salt in cheese

Salt preserves cheese, adds flavor, and firms its texture while reducing moisture.

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Stretching cheese

A technique used in making cheeses like mozzarella where curds are heated and kneaded.

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Cheddaring process

A method of making Cheddar cheese that involves piling curds to reduce moisture.

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Ripening of cheese

The aging process during which cheese develops flavor and texture through microbial activity.

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Soft ripened cheeses

Cheeses like Brie that develop a white crust from Penicillium mould during aging.

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Blue cheese

Cheese inoculated with Penicillium mould, characterized by blue veins and strong flavors.

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Cheese vs. yogurt

Cheese has more extensive protein coagulation than yogurt due to added enzymes.

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Saccharomyces cerevisiae

Yeast used in baking that ferments dough and produces carbon dioxide for rise.

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Vinegar production

Fermentation process where Acetobacter converts alcohol into acetic acid.

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Soy sauce fermentation

A process using soybeans, wheat, and molds/yeasts to create fermented soy sauce.

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Moromi

The mash of koji and salt water used in soy sauce production, fermented with bacteria and yeast.

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Leuconostoc mesenteroides

A bacterium that ferments cucumbers in pickle brine.

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Study Notes

Yogurt Production

  • Yogurt is a fermented milk product
  • Yogurt cultures (bacteria) ferment lactose, producing lactic acid
  • Lactic acid affects milk proteins (casein), impacting yogurt texture and tang
  • Common yogurt cultures are Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus
  • Other lactobacilli and bifidobacteria are sometimes added
  • Some countries mandate minimum microbial counts
  • Western cultures often heat milk (85°C) to denature proteins for optimal setting
  • Heating changes the interactions of Kappa-casein and Beta-lactoglobulin, creating short, branched micelle chains
  • Milk cools to 45°C, yogurt cultures are added and the temperature is maintained for 4-7 hours
  • Nonfat dry milk (NFDM) or scalding milk can increase thickness
  • Milk is incubated at 40-46°C until coagulation by lactic acid
  • Starter cultures (pre-packaged powder or existing yogurt) can be added to milk

Cheese Production

  • Cheese is a coagulated milk product, made from proteins and fat
  • Cheese types vary greatly based on animal, milk pasteurization, fat content, bacteria, molds, processing, and aging
  • Flavoring agents can include herbs, spices and wood smoke
  • Some cheeses contain annatto for color (e.g., Red Leicester) or other ingredients (e.g. black pepper, garlic)

Curdling

  • Curdling is the separation of milk into curds and whey
  • Methods include acidification (using acid or starter bacteria) converting milk sugars to lactic acid and adding rennet
  • Bacteria play roles in the flavor of aged cheeses (e.g. Lactococcus, Lactobacillus, and Streptococcus families)
  • Swiss cheeses use Propionibacter shermani which produces CO2 (creating holes)

Curd Processing

  • Soft cheeses often require no further processing
  • Curds are cut into small cubes in other cheeses for draining
  • Some hard cheeses are heated to 35-55°C to force out more whey
  • Salt preserves, draws moisture, and firms cheese
  • Different techniques like stretching, cheddaring, and washing affect texture and flavour

Ripening

  • Ripening (aging) is the period under controlled conditions and lasts days to years
  • Microbes and enzymes break down casein proteins and milk fat, creating complex flavors and textures
  • Some cheeses introduce additional bacteria or molds during the ageing period
    • Soft ripened cheeses: use Penicillium candidum or P. camemberti mould (white crust, smooth/runny textures)
    • Blue cheeses: use Penicillium roqueforti or P. glaucum moulds (blue veins, assertive flavors)
    • Swiss cheese: Propionibacter consumes lactic acid, producing CO2(holes)

Additional Fermented Foods

  • Yeast (Saccharomyces cerevisiae) ferments dough to rise (producing CO2, alcohol evaporates)
  • Vinegar is produced by Acetobacter aceti oxidizing alcohol to acetic acid
  • Pickles are fermented in brines using bacteria (Leuconostoc mesenteroides, Pediococcus sp)
  • Soy sauce is fermented from soybeans and wheat with the mould Aspergillus oryzae resulting from several bacterial and yeast actions that break down proteins and starch.

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