Beta-casomorphines in yogurt
Place of Publication
School of Science
As a nutritional food, milk is an important source of high-quality proteins, essential amino acids, and unsaturated fatty acids. Milk also contains a number of minor constituents including enzymes, vitamins, minerals, flavor compounds, and bioactive peptides. All of these constituents make important contributions to the nutritional and technological properties of milk and dairy products (Fox and McSweeney, 1998). Cow’s milk proteins contain approximately 80% of casein, consisting of alpha s1-, alpha s2-, beta-, and kappa-casein (αs1-CN, αs2-CN, β-CN, and κ-CN, respectively) (Kopf- Bolanz et al., 2012). Milk proteins play a central role in the formation of texture of cheese and yogurt. In addition, proteins provide a source of essential amino acids and bioactive peptides including angiotensin-converting enzyme (ACE)-inhibitory, antihypertensive, antibacterial, and opioid peptides (Donkor et al., 2007; Minervini et al., 2003; Muguerza et al., 2006; De Noni and Cattaneo, 2010). These peptides are encrypted in an inactive form in parent proteins and may be released by hydrolysis of bacteria-derived enzymes during fermentation of milk and storage of dairy products or digestive enzymes in the gastrointestinal tract (Choi et al., 2012; Sienkiewicz-Szłapka et al., 2009). Beta-caseins (β-CNs) derived opioid peptides were discovered for the first time during in vitro studies by Brantl et al. (1979) and were called beta-casomorphins (BCMs). These days, BCMs have been found in milk, cheese, and fermented milk (De Noni and Cattaneo, 2010; De Noni et al., 2015; Matar and Goulet, 1996; Nguyen et al., 2015a).
The identification of BCMs in dairy products, especially in yogurt, is a challenging task for chemical analysts. This is because yogurt is a complex food matrix containing a large number of proteins and peptides potentially interfering with BCMs. Furthermore, BCMs have been reported at rather low concentrations in yogurt (e.g., sub-ng/g–ng/g level), with BCMs also degrading during yogurt processing, which makes their analytical determination even more challenging (Nguyen, 2016).
This chapter focuses on reviewing the source and the occurrence of BCMs in yogurt and dairy products. The impact of processing conditions such as starter cultures, conditions of fermentation, and storage on the formation/degradation of BCMs during yogurt production is also discussed. In addition, state-of-the-art analytical techniques currently in use for identification and quantification of BCMs are critically discussed on the basis of the most recent scientific literature.