Course:FNH200/Projects/2023/Fermented Milk

Introduction

Fermented Milk refers to the milk that has been allowed to ferment with lactic acid bacteria. The process of fermentation breaks down milk proteins and lactose. Consequently, this will benefit individuals living with milk protein allergies or lactose intolerance. In addition, this process of fermentation extends the shelf-life of milk products.Fermented milk is commonly used during instances of the common cold, diarrhea, eczema, high blood pressure, high cholesterol, irritable bowel syndrome (IBS), and lactose intolerance.

Common Fermented Milk Products

Cultured Buttermilk

Often mistaken for being high in fat, buttermilk is actually the watery by-product of butter making. Cultured buttermilk production starts with pasteurizing skim or low-fat milk at 82-88 °C (180-190 °F) for 30 minutes, or at 90 °C (195 °F) for 2-3 minutes. This process destroys bacteria and denatures proteins to prevent wheying off. The milk is cooled to 22 °C (72 °F) and inoculated with bacteria such as Leuconostoc citrovorum, Leuconostoc mesenteroides, Streptococcus cremoris, and Streptococcus lactis to develop acidity and flavor. After ripening for 12 to 14 hours, the buttermilk is cooled to 7.2 °C (45 °F) to stop fermentation, then packaged and refrigerated.

Sour Cream

The process of creating sour cream follows the same temperature and culture methods described in buttermilk. The main difference is that the starting input is light 18 percent cream.

Yogurt

Similar to buttermilk and sour cream, yogurt differs mainly in bacteria and temperatures. The initial mixture consists of low-fat, skim, or whole milk, fortified with condensed skim or nonfat dry milk. This mixture is heat-treated, cooled to 45.6-46.7 °C (114-116 °F), and then inoculated with equal parts of Lactobacillus bulgaricus and Streptococcus thermophilus. For yogurt with fruit at the bottom, the cultured mixture is poured into cups with fruit, allowed to coagulate for about 4 hours, and then refrigerated. For Swiss or French-style yogurt, the milk is incubated in large tanks, then cooled, blended with fruits or flavors, and packaged for consumption or sale.

Cheese

Illustration of the cheese-making process.

Cheese, a product of specific air temperature, humidity, mold, and milk source conditions, was historically challenging to replicate due to limited microbiology and chemistry knowledge. The process begins by removing water from fresh milk, extending storage life and serving as a preservation method. Pasteurization is often used to slow spoilage, eliminate defects, and destroy pathogens.

Fermentation with microorganisms converts lactose to lactic acid, influencing cheese variety and production. Some cheeses use acid coagulation alone, while others rely on lactic acid or rennet to cause casein proteins to clump and form curds. After curdling, the cheese is cut and gently heated to reduce size and induce shrinking.

Ripening involves enzymes, microorganisms, and curing room conditions, which affect flavor and consistency. Lactose is fermented to lactic acid and then hydrolyzed to form other sugars. Proteins and lipids also break down during ripening. Ripening times vary from one month for Brie to over a year for cheddar. Some cheeses, like Cottage, ricotta, and most mozzarella, do not require ripening.

Kefir

Kefir is a tangy, slightly sour fermented milk drink with a consistency similar to cultured buttermilk. It is made by fermenting milk with kefir grains, which are symbiotic colonies of bacteria and yeasts, including Saccharomyces kefir and Torula kefir. Unlike yogurt, kefir ferments at room temperature due to its mesophilic properties, with lactic-acid bacteria and yeasts doubling every 20 minutes. The flavor comes from various metabolic by-products, including alcohol and carbon dioxide. A second fermentation round can reduce lactose, increase probiotics, or add flavor.

Packaging

The packaging of coagulated and fermented dairy products is crucial for preserving their physical, chemical, and bacteriological properties. Commonly used materials include glass, polyethylene, low-density polyethylene (LDPE), high-density polyethylene (HDPE), Ethylene vinyl alcohol, polyvinylidene chloride (PVDC) and tetrapak.

Example of aluminum foil used for cheese packaging.

Different dairy products require specific packaging considerations. For yogurt, fruit aromas can affect the brittleness of polystyrene packaging, and fruit acids can cause pitting in untreated aluminum lids. Therefore, polystyrene tubs are commonly used for their practicality and cost-effectiveness.

Buttermilk and sour cream are typically packaged in LDPE sachets, wax-coated paper cups, polystyrene cups, and polypropylene cups, avoiding high-impact polystyrene (HIPS) due to the risk of cracking from free fatty acids.

Example of PVDC coated plastic film cheese packaging.

Cheese packaging must prevent moisture loss, provide protection, and block microorganisms and oxygen. High-moisture, high-fat cheeses require packaging that prevents mold growth and oxidation, often using sealed containers in a vacuum or inert gas atmosphere. Processed cheeses use aluminum foil, while other cheeses use PVDC-coated plastic films for moisture and oxygen barriers. Kefir, with its active microbes, also requires special packaging. Studies show methallized oriented polyester film (MOPET) is most effective, but due to preparation costs and consumer challenges with freeze-dried kefir, polyethylene film packaging is preferred for its economic and practical advantages.

Role of Lactic Acid Bacteria

Different types of strains of lactic acid bacteria include but are not limited to: Lactobacillus, Lactococcus, Leuconostoc, Fructobacillus, Weissella, Pediococcus, Enterococcus, Streptococcus, Carnobacterium, and Oenococcus.

Lactic acid bacteria are very resistant, and can tolerate low pH, heat treatments, and concentrations of salt.

Flavor

The variety in fermented milk products results from different technologies and lactic acid bacteria strains. In cheese production, starter cultures produce acid during manufacturing and aid in ripening, while non-starter cultures, active in the secondary phase, also contribute to ripening but not acid production. Flavor formation involves both types of LAB and the metabolic pathways of lactose, lactate, and citrate, as well as lipolysis releasing free fatty acids.

Texture Development

In yogurt, the role of lactic acid bacteria is essential to develop the desired texture. some LAB, depending on strain, produces the exopolysaccharides (EPS), a viscosifying agent that helps provide the soft and thicker texture found in yogurt. In addition, the formation of acid by lactic acid bacteria contributes to coagulation through its neutralization effect on milk proteins. The production of exopolysaccharides, acidification of milk, and proteolytic activities on milk proteins enables for the generation of flavor and texture.

Preservation

The presence of lactic acid bacteria (LAB) in milk fermentation is important as it produces acid that function as preservative agents and contribute to flavor. Milk and fermented milk products are very favorable substances for the growth of microorganisms. The functional capability of lactic acid bacteria to produce acid functions as a preservative property, exhibiting antimicrobial activity. Thus, acidification of milk defeats against proliferation of pathogens as well as spoilage microorganisms.

Labelling Requirements for Dairy Products

According to Canadian Food Inspection Agency: https://www.inspection.gc.ca/en/food-labels/labelling/industry/dairy(link in module 4.3), we conclude the following:

Label Basics:

1. Common Name: The product name must be clear and follow a standard format, or indicate any differences (e.g., "Lactose-Free Milk").
2. Additional Descriptors: Products may require extra details, such as "salted butter" to indicate salt presence. Firmness and ripening characteristics must be noted based on moisture content and ripening.
3. List of Ingredients: Ingredients must be listed according to Canadian prepackaged food regulations, using standardized terms and specific declarations for dairy ingredients.
4. MicroGARD Ingredient: If MicroGARD is included, its common names must appear in the ingredient list.
5. Net Quantity: The amount of product must be clear in grams or milliliters. For items over 20g sold as a unit, the common name and quantity of each item must be stated along with the total net quantity.
6. Name & Place of Business: The label must identify the company responsible for the product.
7. Origin: Imported products must state "Product of (Country)" in bold, at least 16mm high.

Important Details:

1. Percent Milk Fat and Moisture: Indicates the product's composition and nutritional profile.
2. Best Before & Storage: Essential for safety and quality due to perishability.
3. Nutrition Facts Labeling: Required for most dairy products except single portions for restaurants. Products with high sodium, sugars, or fat must include the nutrition information if exceeding thresholds.
4. Serving Size: Typically shown in household and metric measures, such as per 50g.
5. Grade Name: Optional, but some products may display grades like "Canada 1" to indicate they meet specific standards.

Regulations

There are some general food regulations need to be followed when products are sold.

According to the Canadian Food and Drugs Act section 4.1,

No person shall sell an article of food that

• (a) has in or on it any poisonous or harmful substance;
• (b) is unfit for human consumption;
• (c) consists in whole or in part of any filthy, putrid, disgusting, rotten, decomposed or diseased animal or vegetable substance;
• (d) is adulterated; or
• (e) was manufactured, prepared, preserved, packaged or stored under unsanitary conditions.

Exam Question(s)

Based on our research, we proposed two possible exam questions: one cohesive and within our course material that offers new insights, and another that introduces new packaging materials discussed in the project but relates to the main concept of packaging.

[1] Some cheese varieties are produced through the coagulation of milk without using rennet.

Correct Answer: True

Explanation of Answer & Reason to be on the Final Exam:

Before this project, I assumed all cheesemaking involved rennet to solidify milk, as we learned extensively about rennet in class. However, I was surprised to learn that some cheeses rely solely on acid coagulation, as discussed in the Common Fermented Milk Products - Cheese section. Fermentation produces lactic acid, lowering the milk's pH and causing casein proteins to form curds. Fresh cheeses like ricotta are made this way. This topic is ideal for the final exam because it challenges a common misconception from our class and highlights the diversity of cheesemaking techniques. Different methods, using rennet, acid coagulation, or both, create a variety of cheese textures and flavors.

[2] Which of the following packaging materials is NOT commonly used for fermented dairy products due to the risk of cracking from free fatty acids?

a) Low-density polyethylene (LDPE)

b) High-impact polystyrene (HIPS)

c) Polypropylene

d) Wax-coated paper

Correct Answer: b) High-impact polystyrene (HIPS)

Explanation:

Before the team project, I hadn't considered the impact of free fatty acids on packaging. I was surprised to learn that HIPS, a seemingly robust plastic, can crack when exposed to these acids in fermented dairy products like buttermilk and sour cream. This aligns with our course content on packaging, highlighting the importance of selecting materials to ensure quality and prevent spoilage. Understanding chemical interactions between food components and packaging is crucial in food science, so we suggest including this question on the exam.