Hydrolysis of whey proteins beta-lactoglobulin and alfa-lactalbumin by lactic acid bacteria

MICAELA PESCUMA; ELVIRA MARÍA HÉBERT; FERNANDA MOZZI; GRACIELA FONT DE VALDEZ

Badajoz, España

Conferencia; International Conference on Environmental, Industrial and Applied Microbiology; 2005

BioMicroWorld

Lactic acid bacteria (LAB) have been widely used as starter cultures for the manufacture of fermented products. Whey, the milk serum produced during the elaboration of cheese, is a nutritionally superior ingredient with desirable physicochemical attributes. Whey powder is composed of about 80% of lactose and 10% of protein; b-lactoglobulin (58%) and a-lactalbumin (13%) being the most prevalent protein fractions in whey. Other less abundant whey proteins are immunoglobulins, serum albumins and proteose peptones. During recent years, interest has grown on the nutritional properties of whey proteins. Although b-lactoglobulin is an important source of essential aminoacids, its globular structure makes it stable against the acids and proteolytic enzymes present in the stomach. This stability, which is relevant as a retinol carrier in cows, converts it into a non-digestive protein by man. a-lactalbumin is biologically important since it is involved in the biosyntesis of lactose, which is an energy source for newborns. The aim of this work was to analyse the proteolytic activity using the o-PA method [1] and densitometric analysis (QuantiScan program) of Tricine SDS PAGE gels [2]) of 16 LAB strains in pasteurised reconstituted whey (PRW: 10 and 16% w/v). The proteolytic activity of the microorganisms (commonly used in the manufacture of fermented milk products): Lactobacillus acidophilus (3), L. casei (5), L. debrueckii subsp. bulgaricus (3) and Streptococcus thermophilus (5) were evaluated at 37ºC after 24 h of incubation. All the LAB tested were able to hydrolyse whey proteins, although the results were strain dependent and variable respect to the PRW concentration used. The proteolytic activity measured by o-PA, indicated that the strains belonging to the St. thermophilus group were the lest proteolytic microorganisms with values between -0.18 and 0.15 mmol leu/ml and 0.1-0.65 mmol leu/ml in PRW 10 and 16%, respectively. L. bulgaricus CRL 870 with o-PA values of 2.4 mmol leu/ml (PRW 10%) and 3.9 mmol leu/ml (PRW 16%), and L. acidophilus CRL 745 with 1.9 mmol leu/ml (PRW 10%) and 3.3 mmol leu/ml (PRW 16%) were the most proteolytic strains. The proteic fraction, b-lactoglobulin was, the least hydrolysed from the total with the highest degradation percentages (58% and 18%) corresponding to L. casei CRL 116 and L. acidophilus CRL 636, respetively. On the contrary S. thermophilus CRL 817 was not able to degrade it. a-lactalbumin was, in general, easier to degrade by all strains with a degradation percentage range between 6.8 and 42. From these results we suggest that L. casei CRL 116 and L. acidophilus CRL 636 could be included in a starter culture for the development of a whey based fermented product.