MICROBIOLOGY Textbook - 2012

CHAPTER 15. FOOD MICROBIOLOGY

15.1. MICROBIOLOGY OF MILK AND DAIRY PRODUCTS

15.1.4. Butter

Butter is a milk fat concentrate. Depending on the moisture mass fraction in the finished product, butter is classified into sweet-cream butter (16% moisture), amateur butter (20%), peasant butter (25%), and sandwich butter (35%). Butter is produced as sweet-cream or cultured (sour-cream), salted or unsalted, and with various additives.

Milk fat, the primary component of butter, is a hard-to-reach nutrient source for most microorganisms. Only microorganisms with active lipases can utilize milk fat as a nutrient source. These are predominantly pseudomonads and Molds. Microbiological processes occur mainly in the butter plasma, which contains Proteins, lactose, and minerals. Butter with finely dispersed and evenly distributed moisture is less susceptible to microbiological spoilage and exhibits greater storage stability. The absence of bacterial proliferation in small plasma droplets is due to the Water within them being bound to the substances of the fat globule membranes, making it unavailable to microorganisms.

The quality and storage stability of butter largely depend on the quality of raw Materials and manufacturing conditions. The primary sources of the initial microflora in butter include cream, equipment, water, air, salt, packaging materials, flavor additives (sugar, cocoa, coffee, etc.), starter cultures (for cultured butter), and containers.

Sweet-cream butter is produced without the participation of microorganisms; therefore, any microbiological activity within it leads to flavor and aroma defects and, ultimately, to product spoilage.

Cream is pasteurized at 92–95 °C without holding, so the residual microflora count is low, amounting to several thousand Cells per 1 cm³. Spore-forming Bacteria predominantly survive pasteurization in the cream. To obtain butter with a low microbial count, it is essential to strictly adhere to Sanitary and hygienic production standards and prevent recontamination of pasteurized cream at all Stages of the process. The microflora of sweet-cream butter consists of the residual pasteurized cream microflora and microorganisms introduced during the manufacturing process. The main representatives of extraneous microflora in sweet-cream butter include lactic acid bacteria, spore-forming proteolytic bacteria, pseudomonads, coliforms (coliform bacteria), Yeasts, and molds. The total microbial count in fresh butter can range from 10⁴ to 10⁶ per 1 g. The progression of microbiological processes in butter depends on its storage Temperature. At low positive temperatures (5–8 °C), bacteria of the genera Pseudomonas, Alcaligenes, Flavobacterium, as well as micrococci and yeasts, can multiply, causing the microbial count to increase by two orders of magnitude after just 3–5 days of storage. Therefore, sweet-cream butter should be placed in low-temperature refrigeration chambers immediately after production. At storage temperatures ranging from –15 to –18 °C, microbiological processes are inhibited, and the microbial count during storage not only remains stable but gradually decreases.

Cultured (sour-cream) butter is produced by fermenting cream with a starter culture containing mesophilic lactococci and leuconostocs: Lactococcus lactis ssp. lactis, Lac. lactis ssp. cremoris, Lactococcus lactis ssp. diacetylactis, Leuconostoc mesenteroides ssp. cremoris. There are two Methods of cream Fermentation: long and short. As a result of lactic acid bacteria METABOLISM, cultured butter acquires a specific fermented milk taste and a pleasant aroma due to the accumulation of lactic acid and Aromatic Compounds (diacetil, acetaldehyde, volatile Fatty acids, etc.).

The microflora of cultured butter is represented primarily by lactic acid bacteria. The count of lactic acid bacteria can range from 10⁶ to 10⁸ per 1 g, with significantly higher numbers in butter produced with long-term fermentation compared to short-term fermentation. The volume of extraneous microflora is negligible, and its growth is restricted by the generated lactic acid.

Butter defects are typically the result of extraneous microbial activity or chemical oxidation. Microorganisms can cause the following defects that develop during storage.

Sour taste in sweet-cream butter is observed when the plasma acidity exceeds 23 °T, which is a consequence of storing the product at elevated temperatures (above 10 °C). In cultured butter, an excessively sour taste manifests when plasma acidity exceeds 55 °T. The cause of this defect is the proliferation of lactic acid rods in the butter plasma. Another cause of a sour taste can be The Use of raw materials with elevated acidity in production.

Rancid taste and odor arise from The breakdown of milk fat by microbial lipolytic Enzymes remaining in the cream after pasteurization. Rancid flavor also appears in butter made from cream that has been stored in a chilled state for extended periods. Bacteria of the genera Pseudomonas, Achromobacter, as well as certain species of yeasts and molds, possess the most active lipases. The milk fat decomposition process occurs in two stages: in The First stage, fat Hydrolysis takes place under the action of lipolytic enzymes, leading to the accumulation of fatty acids (butyric, caproic, caprylic) that impart a pungent odor and rancid taste to the butter. In the second stage, these Fatty acids are oxidized to form aldehydes, ketones, esters, and other substances that intensify the defect.

Cheese-like taste and odor are caused by the accumulation of a specific amount of n-valeric acid as a metabolic product of proteolytic bacteria or their enzymes. The accumulation of other low-molecular-weight volatile acids also contributes to this defect. The defect develops in butter during storage at low positive temperatures.

Putrid, musty, unclean taste. This defect occurs most frequently in sweet-cream butter and is caused by the breakdown of Plasma Proteins with the accumulation of degradation products due to the proliferation of putrefactive bacteria. In the initial stage, an unclean taste appears in the butter. Subsequently, a musty taste and odor develop, followed by a pronounced putrid taste. Contributing factors include insufficiently high cream pasteurization temperatures, storing cream at low temperatures prior to churning, and poor sanitary and hygienic standards in production.

Staff (surface oxidation/greasiness). The Essence of this defect lies in The formation of a transparent, dark-yellow layer On the surface of the butter block, which has a specific odor and an unpleasant bitter or cloyingly pungent taste. The formation of staff is accompanied by a sharp increase in plasma plasma acidity, an elevated peroxide value, an increase in soluble nitrogen compounds, and a decreased iodine number. Staff occurs as a result of glyceride polymerization and milk fat oxidation driven by dehydration and the proliferation of psychrotrophic proteolytic bacteria. Sunlight, high moisture permeability of packaging materials, and heavy metal salts catalyze the formation of staff.

The occurrence of this defect can be prevented by reducing the air content in the butter, increasing the degree of moisture dispersion in the butter plasma, using light- and moisture-impermeable packaging materials, and storing the butter at low negative temperatures.

Molding is one of the most common butter defects. Molds can multiply both on the surface and inside the bulk of the butter. Surface molding is caused by mold Fungi of the species Penicillium glaucum, Endomyces lactis, Aspergillus glaucum, Trichoderma lignorum, Alternaria spp. Mold fungi secrete lipases and proteinases that break down milk fat and plasma proteins. Consequently, alongside a moldy taste, a rancid off-flavor appears in the butter. Internal molding occurs within butter blocks that have loose packing. The microaerophilic bunch mold Cladosporium herbarum proliferates in the resulting voids. Storage temperature and air humidity strongly influence the growth of mold fungi. At temperatures near 0 °C, mold growth is arrested, and at —11...—18 °C with an 80% relative humidity, it ceases entirely. A sodium chloride concentration of 1.5–2.0% in salted butter inhibits The Development of mold fungi.

To prevent mold growth, it is necessary to improve sanitary and hygienic production conditions, thoroughly clean and disinfect equipment, utensils, and tools, strictly observe pasteurization regimens, and monitor the microbiological purity of the air in production shops and storage chambers. Molding can be prevented through proper butter Processing, dense packing of the bulk block, packaging in polymer films, rapid and deep chilling, and storing the finished product at low negative temperatures (—18...—25 °C) and low relative humidity (not exceeding 80%).