A comparative study of proteolysis in cheddar cheese and yeast-inoculated cheddar cheese during ripening

Abstract

English: Proteolysis is regarded as the most important event in the ripening of Cheddar cheese to contribute to the development of flavour. The characteristic proteolysis of each type of cheese is brought about by the enzymes used in the manufacturing process, e.g. rennet, as well as enzymes from the specific microbial cultures used in each cheese type. The effect of an inoculated yeast, Oebaryomyces hansenii, and its enzymes on proteolysis in Cheddar cheese was investigated. Proteolysis and development of peptides of the yeast-inoculated Cheddar cheese was followed throughout the ripening process and compared to the proteolysis in a standard Cheddar cheese. In a sensorical comparative study, no difference was found by a consumer panel between the two types of cheese, nor was any of the two significantly preferred. An expert panel however, judged the yeast-inoculated Cheddar cheese to be bitter. The proteins and peptides from the cheeses were extracted and fractionated by virtue of differences in solubility and molecular size. Yeast-inoculated Cheddar cheese contained less water-soluble nitrogen indicating a difference in proteolysis between the two types of cheese. Urea-polyacrylamide gel electrophoresis of the waterinsoluble fraction indicated that in the yeast-inoculated cheese rennet hydrolysis of o.si-casein was increased with faster formation of one primary peptide, o.s1-1as well as (o.s1-CN(f102-.)), with little further hydrolysis. The ~-casein was hydrolyzed slowly but with several additional peptides occurring. Reversed-phase high performance liquid chromatography of the watersoluble fraction indicated that a different peptide profile was formed, with at least five unique peptides at high amounts.

Afrikaans: Proteolise word gereken as die belangrikste gebeurtenis in die rypwording van Cheddarkaas om by te dra tot die ontwikkeling van geur. Die karakteristieke proteolise in elke tipe kaas word veroorsaak deur ensieme betrokke in die vervaardigingsproses, nl. rennien, asook die ensieme afkomstig vanaf die spesifieke mikrobiese kultuur gebruik in elke kaas variëteit Die effek van 'n geïnokuleerde gisspesie, Oebaryomyces hansenii, en sy ensieme, op proteolise in Cheddarkaas is bepaal. Proteolise en die ontwikkeling van peptiede in die gisgeïnokuleerde Cheddarkaas is gevolg tydens die rypwordingsproses en vergelyk met die proteolise in 'n standaard Cheddarkaas. Tydens 'n sensoriese, vergelykende studie deur 'n verbruikerspaneel is geen verskil gevind tussen die twee tipes kaas nie en is geen kaas bo die ander verkies nie. 'n Opgeleide paneel het egter die gis-geïnokuleerde kaas as bitter beoordeel. Die proteïene en peptiede is geekstraheer en gefraksioneer vanuit die kaas op grond van verskille in oplosbaarheid en molekulêre grootte. Gis-geïnokuleerde Cheddarkaas het 'n laer inhoud water-oplosbare stikstof bevat en dien as 'n indikasie van die verskil in proteolise tussen die twee tipes kaas. Ureum-poliakrielamied gel elektroforese gedoen op die water-onoplosbare fraksie het gewys dat rennien-hidrolise van aS1-kaseïn versterk is in die gis-geïnokuleerde kaas deur die vinnige vorming van die primêre peptiede aS1-1asook as1- CN(f102-e), met 'n geringe verdere hidrolise. Die ~-kaseïne is stadig gehidroliseer, maar met verskeie addisionele peptiede gevorm. Tru-fase hoë druk vloeistof chromatografie van die water-oplosbare fraksie het 'n ander peptiedprofiel getoon, met ten minste vyf unieke peptiede teenwoordig in groot hoeveelhede.