NUTRIENTS IN CHEESE
In recent days, the overall consumption of fluid milk shows a gradual decline, with a steady increase in consumption of cheese in most of the countries. The growth of cheese consumption can be favourably compared with that of growth in milk production which is approximately 4% during 2011.
The fat content in the cheese milk is adjusted to different levels so that cheese of different varieties containing varying levels of fat can be produced. Cheese, when it is fresh has a fat content of up to 12% level. The fat content in the ripened cheeses generally range between 20 and 30%. Consumers generally prefer high fat cheeses due to high fat content and this imparts a better flavour to the cheese. The fat in the dry matter content of cheese should be at least 40-50%, like Cheddar cheese so that there will be sufficient fat in the body which contributes to the typical aroma during cheese ripening by fat breakdown or lipolysis. With increasing consumer awareness about health and ill effects of excess fats, it becomes prudent to go in for "low fat cheese varieties".
However, the low fat cheese varieties should have sufficient fat so that it will be organoleptically acceptable. Pasteurization of milk inactivates the native lipase and hence has no role to play in the cheese ripening. It is the microbial lipases which play a predominant role in the cheese curing. The concentration of free fatty acids in cheese shoots up to 1-5 g / Kg because of liopolysis. There exists a positive correlation between the content of free volatile fatty acids and the flavour.
One need not bother about the cholesterol content of the cheese as it is rather low varying between 0-100 mg / 100 g depending on the amount of fat present in the cheese. Hence contribution of the cheese towards the cholesterol intake would be very limited to 3-4%. Cholesterol present in the diet plays a limited role to boost the blood cholesterol. The body has its own check to decrease the cholesterol synthesis when ever the dietary cholesterol level exceeds certain limit. The digestibility coefficiency of the fat found in different varieties of cheese varies between 88-94%.
The higher amount of biologically valuable proteins in the cheese adds to its nutritive value. The protein content of different varieties of cheeses generally varies between 20-35%. The protein content varies inversely with the fat content in any type of cheese. A 100 g piece of a soft cheese will meet 30-40% of the daily protein requirement of an adult human being and from 100 g of hard cheese, 40-50% can be met. During the cheese manufacture casein, the major milk protein is incorporated to 95% level in the cheese whereas most of the biologically valuable whey proteins pass into the whey portion. Hence only 75-80% of the total protein is harvested in the cheese. 4-6% of the total protein is formed by whey protein when pasteurized milk is utilized for cheese making.
The biological value of protein obtained from cheese is somewhat less than that of milk since the nutritionally superior whey proteins (containing sulphur containing amino acids) are excluded during cheese making. The PER values for cheddar cheese is 3.7 which is significantly higher than that for casein (2.5). If an index of 100 is given for the essential amino acids present in milk, then the corresponding values for the different cheese varieties varies between 91 and 97.
The biological value of protein is least influenced by the enzymes utilized during the preparation of cheese making (like rennet accompanied by acid production) or employed during ripening. The Maillard reaction does not occur in the cheese making and hence all the lysine available in milk is made available in cheese.
Some of the ripened cheeses show a higher PER values than that of milk from which it is prepared. When ultrafiltration is done to concentrate cheese milk, the whey proteins are incorporated into the cheese milk (in the ordinary process, they are lost in the whey) thereby improving the nutritive value of the cheese. The whey proteins constitute about 15% in such types of cheese. Cheese serves as a storehouse of essential amino acids, having similar proportion of essential amino acids that is present in milk except the methionine and cystine. During the ripening of cheese, part of the water-insoluble casein is converted into water-soluble nitrogenous compounds including the intermediate products of protein hydrolysis and free amino acids.
Digestion of protein is greatly improved during the curing process and hence ripening can be rightly referred to as “PREDIGESTION” step. A number of cheese varieties show an almost 100% true digestibility. As for as protein digestibility is concerned, it is better in cheese (96-97%) than in milk (92%). Small peptides are capable of passing through the walls of the intestine and it is assumed that they can penetrate through the intact cell membranes so that they are directly available for the cell. The free amino acids particularly, aspartic and glutamic acids are said to promote the secretion of gastric juices. There is no mention of food allergy arising from cheese protein.
The amines that are produced during cheese ripening by decarboxylation of free amino acids will be sometimes physiologically active. The principal amines that are found in cheeses are histamine, tyramine, tryptamine, putrescine, cadaverine, and phenyl alanine. Tyramine and phenyl alanine have hypertensive and histamine has hypotensive effect. However, mono and diamine oxidases convert the biogenic amines into aldehydes and finally into carboxylic acids by oxidative deamination. The threshold of the toxicity levels for these biogenic amines may vary depending on the individuals and healthy persons are capable of metabolizing the amines even when large quantities of cheeses are consumed.
Some persons are prone to migraine attack after consuming cheese. It is assumed that such people suffer from a genetically determined lack of monoamine oxidase. Consumption of large quantities of tyramine (up to 100mg) in these patients will cause migraine.
LACTOSE AND LACTIC ACID
There is practically no lactose present in cheese and if at all it is present, in very low concentration (1-3g/100g) because most of the lactose present in milk passes into the whey and that retained in the cheese curd is converted into lactic acid during the ripening process. Hence, cheese is considered as a suitable diet for people suffering from lactose malabsorption and diabetes.
Cheese usually contains both isomers L(+) and D(-) of lactic acid. During storage, the L(+) isomer is converted to D(-)isomer, the relative proportion of the type varies depending on the type of starter culture used and some other ripening factors. D(-) lactic acid can be metabolized by the human beings only to a certain extent by the a specific mitochondrial enzyme. However, the findings of the recent research shows that the toxic effect of D(-) lactic acid cannot derived for the adolescent or adult. The world health organization has not given any admissible intake for adults while for infants up to one year of age, it is recommended to provide a diet free from D(-) lactic acid.
100g of soft cheese will supply 30-40% of the daily calcium requirement and 15-20% of the daily phosphorous requirement. 100g of hard cheese will completely meet the daily Ca requirement and half of Phosphorous requirement. The calcium, phosphorous and magnesium in cheese are utilized as well by the body as that of milk. The changes (both physical and chemical) that occur in the cheese during the manufacture and ripening do not affect the bioavailability of calcium.
The ratio of calcium and phosphorous available in the cheese is nutritionally superior and favours absorption by the body. Cheese is one of the foods that is non-carcinogenic. The wide fluctuation in the sodium content of cheese is attributed to the varying level of salt addition during the manufacture. The cheese contributes to only 5% of the total sodium intake. Nevertheless, a restricted sodium intake is often recommended to accommodate the diets of consumers under medical management suffering from hypertension.
Processed cheeses are considered as a major source of trace elements especially aluminium as these varieties contain a higher aluminium level when compared to other types. The selenium content of cheese range between 5 and 12 microgram per 100g of cheese. The nickel content varies between 2 and 34 microgram per 100g. The mercury levels in the cheese are far lower than that is permitted (0.04-0.16 microgram per 100g). Milk proteins does not affect the absorption of iron.
The concentration of fat soluble vitamins in cheese is dependent on the fat content. About 80-85% of the Vitamin A present in milk is passed on to cheese. The water soluble vitamins are transferred to a lesser extent. The milk contains higher concentration of Vitamin B complex so that it almost carried over to Cheese which serves as a good source of the same especially for Vitamin B12 and B2. Some of the mould ripened cheeses contain more of the B vitamins than other types of cheeses.
The concentration of B vitamins continuously undergo change during cheese ripening since they are both used up and synthesized by the cheese microflora. After long storage of ripening, the concentration of B vitamins increases and the types of microflora involved in ripening play a major role in synthesis of a particular vitamin. The individual microorganisms present in the cheese are capable of synthesizing niacin, folic acid, biotin and pantothenic acid. Propionic acid bacteria are responsible for the synthesis of vitamin B12. On the other hand, most of the ascorbic acid degrades during ripening.