Masters Degrees (Microbial, Biochemical and Food Biotechnology)

Permanent URI for this collection

http://hdl.handle.net/11660/447

Browse

Browsing Masters Degrees (Microbial, Biochemical and Food Biotechnology) by Advisor "De Wit, M."

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Enzymes from yeast adjuncts in proteolysis during cheddar cheese ripening
    (University of the Free State, 2007-11) Amos, Lize-Mari; Osthoff, G.; De Wit, M.
    A great deal of research in cheese technology is devoted towards the manipulation of glycolysis, lipolysis and proteolysis in order to accelerate ripening times or to improve flavour. There is increasing evidence that certain yeast species contribute to flavour and texture development during ripening of certain cheeses, including Cheddar cheese. The addition of yeast cultures as adjunct cultures may accelerate ripening, or lead to a faster development of flavour and taste. This is brought about by an increase in primary proteolysis of the caseins as well as the break down of amino acids into flavour compounds. The respective enzymes involved seem to be proteases with plasmin or plasmin activator activity, and glutamate dehydrogenase. This research reports on the inclusion of yeasts as adjuncts in the processing of Cheddar cheese. Yeasts that expressed both enzyme activities were added as single adjuncts, while combinations of yeasts with singular enzyme activity were employed. Changes during ripening were monitored by sensory and biochemical analyses. The latter includes proteolysis, lipolysis and enzyme activity.
  • Thumbnail Image
    ItemOpen Access
    Fruit quality of South African cactus pear cultivars
    (University of the Free State, 2010-06) Rothman, Anna Maria Petronella; De Wit, M.; Bothma, C.
    English: The cultivation of cactus pears requires low input and it has been grown widely in drier areas of South-Africa as fodder crop, particularly for times of serious drought. Cactus pears also serve as a source of inexpensive nutritious food for lower income groups Sugar is the main determent of taste of the cactus pear cultivar and content value range from 10 °Brix to 17 °Brix. Glucose is the predominant sugar with fructose as the second sugar, thus the fruit pulp is very sweet. The pulp of the cactus pear cultivar consists of a high pH value (> 4.5) and low acidity level (0.03-0.12 % ), (SaenzHernandez, 1985; Brutch, 1993; Piga, 2004; Salim, 2009). The aim of this study was to determine the fruit quality of cactus pear fruit. Physical/chemical and sensory quality attributes were evaluated for two agricultural seasons ( 2007 and 2008). The influence of factors such as rainfall and temperature on quality was determined. Furthermore, sensory analysis was used to distinguish among the available 33 cultivars, not only for their taste, but also to establish the cultivar most stable to varying environmental conditions. This study determined whether sensory quality of cactus pear fruit was influenced by the physical/chemical parameters by correlating the physical/chemical data with the sensory analysis. There were highly significant differences observed in terms of physical/chemical composition (p < 0.001) among 33 different cactus pear cultivars in South Africa, for seasons 2007 and 2008. This finding indicated that genetic differences among cultivars as well as seasonal changes have a significant influence on fruit quality. It was evident from this study that not only the cultivar and agricultural season, but also the interaction between the cultivar and season had significant influences on fruit quality. The best preferred cultivar, regarding physical/chemical fruit quality attributes, was Nudosa, performing the best regarding fruit mass and pulp glucose. Messina performed the best regarding 0 Bx. Nudosa and Messina performed the best regarding pulp fructose content, while Blue Motto had the best acidity levels (pH and TA). Sensory analysis, used to determine whether the consumer could distinguish among the available 33 cultivars was done by using the FCP technique and it was clear that the consumers could only successfully distinguish between the two seasons (77.72 %) , but not among the 33 different cactus pear cultivars. The fodder cultivar, Robusta, was an exemption and could be clearly distinguished from the other 32 cultivars. The sensory quality of cactus pear fruit obtained from the consumers was indeed influenced by the physical/chemical parameters. Cultivars like Robusta, Fresno and Nudosa had been significantly influenced by seasonal differences. The physical/chemical data and the sensory attributes were correlated.