گلیسیری پروتئین های پنیر: پیامدهای فن آوری و تغذیه ای Glycation of whey proteins: Technological and nutritional implications

1-Introduction Thermal treatment is a basic step in the processing of milk and milk products in order to control the safety and quality of the obtained products. The severity of the thermal processing ranges from the mild thermization applied directly to raw milk at the dairy farm up to sterilization of evaporated and condensed milk. Several chemical changes usually occur in thermally treated milk [1] resulting in variable losses in vitamins and enzymes, denaturation of milk proteins and interaction between lactose and milk proteins to form protein-sugar conjugates. The interaction between lactose and milk proteins has received special interest since the early studies on milk processing, whereas it has diversified effects on the digestibility, and nutritional, functional and conformational changes in milk proteins as well as the quality of dairy products. During storage, further changes occur in the formed lactosemilk protein conjugate depending on the storage conditions. Over the years research [2,3,4] has been extended to study conjugation of milk protein with various carbohydrates aiming for better understanding the mechanism of protein-carbohydrate conjugation and to produce milk protein products of modified functionality and antigenicity. Whey proteins are a group of globular proteins representing 20% of the total proteins of bovine milk and almost the total proteins of whey [5]. The main proteins in whey and their concentration (relative to the total whey proteins) are β-lactoglobulin (~ 55%), αlactalbumin (~ 20%), blood serum albumin (~7%), immunoglobulins (~13%) and minor proteins (~ 5%). In addition, whey obtained from cheese manufacture contains the casein glycomacropeptide (GMP) which arises from the action of chymosin on κ-casein. There has been a global increase in the production and utilization of whey protein products due to the increase in cheese production and concentration of whey. An annual increase in cheese production of 2.6% has been reported by IDF [6]. Also, the advent of powerful industrial technologies for the separation of whey proteins based on membrane and ion exchange methods has enabled the dairy industry to produce whey protein products of tailored composition and functionalities. It has been estimated that the manufacture of whey protein products can increase the revenue of a cheese factory by 11%. The world-wide market [7] value for whey powders and protein ingredients amounted to US$ 9.8 billion in 2013 and has been projected to reach a value of $11.7 billion in 2017 [8]. Of the 31 million tons of the dried whey products produced in the USA, about one fifth has been whey protein isolates [9]. The demand for whey proteins has been boosted by the consumer awareness on its impact of food on human health, the documented nutritional and health properties of whey proteins [10], and consumer demand for high-protein foods and supplements.