LD2668 .T4 1966 E38 / Master of Science

Call number: LD2668 .T4 1978 B33 / Master of Science

Call number: LD2668 .T4 1978 O39 / Master of Science

Call number: LD2668 .T4 1979 M33 / Master of Science

Growth of spoilage fungi in bread and other bakery products is currently controlled with the addition of weak acid preservatives. Consumers demand more natural products and thus there is a need to reduce the amount of chemical preservatives added to foods, or to identify alternative, more 'natural' antifungal compounds with strong biological activity. This thesis reports on several areas of research undertaken in the project: evaluation of sub-optimal concentrations of existing preservatives, under different environmental conditions, on growth and ochratoxin A (OT A) production by six bread spoilage moulds; efficacy of new/natural antifungal compounds for possible use in bread preservation; evaluation of the impact of preservation hurdles on ecophysiology of the spoilage fungi, including niche overlap; and mechanisms of action of preservatives on hydrolytic enzymes. It was found that the use of currently applied levels of the existing preservatives potassium sorbate, calcium propionate and sodium benzoate were effective, under low pH environments (pH 4.5) at completely controlling growth of spoilage moulds (Aspergillus ochraceus, Eurotium repens, Cladosporium herbarum, Penicillium corylophilum and Penicillium verrucosum) on wheat flour-based substrates over a period of 30 days. At higher pH levels, the efficacy decreased being almost nil at pH 7.5. The use of sub-optimal concentrations of weak acid preservatives led in most cases to reductions in lag times and/or stimulation of mould growth and ochratoxin A production by P. verrucosum strains. Cont/d.

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Thesis presented in partial fulfilment of the requirements for the degree of Master of Technology (Food Technology) Department of Food Technology Faculty of Applied Sciences 2014 / The aim of this study was to evaluate the effect of transglutaminase (TG) and cyclodextrinase (CG) on the rheological characteristics of oat dough and shelf-life characteristics of oat bread with a view to developing oat bread with improved texture and shelf-life. Firstly, the effects of yeast, carboxylmethylcellulose (CMC), plain yoghurt (YG), transglutaminase (TG) and cyclodextrinase (CG) on the mixing, pasting, thermal, quantification of free amino acid groups and protein crosslinking properties of oat dough were investigated through a 25-2 fractional factorial design resolution III with yeast (1.25, 3.25%), CMC (1, 2%), YG (10.75, 33.75%), TG (0.5, 1.5%) and CG (10, 40 μl) as independent variables. Among all the ingredients, only CMC, YG, and TG exhibited significant (p < 0.05) effects on the mixing properties of oat dough while yeast and CG slightly affected it. TG addition increased water absorption (34.80 - 38.45%) and peak resistance (696.40 - 840.30 FU) but decreased the dough softening (93.20 - 67.75 FU) as its level varied from 0.5 to 1.5 g. CG did not significantly (p > 0.05) affect the mixing properties of oat dough. As its level increased from 10 - 40 μl, the water absorption (38.45 - 34.80%), energy at peak (11.45 - 3.75 Wh/kg), peak resistance (840.30 - 696.40 FU) slightly decreased while the softening of oat dough increased from 67.75 to 93.20 FU. The addition of yeast and YG showed significant (p < 0.05) impacts on the pasting properties of oat dough compared to CMC, TG and CG. The storage modulus of oat dough was slightly (p > 0.05) increased by adding TG (180.37 - 202.78 kPa) and CG (170.75 - 175.71 kPa). TG decreased the loss modulus (65.95 - 62.87 kPa) of oat dough while CG increased it from 62.01 - 64.61 kPa. The thermal properties of oat dough were slightly affected by all the ingredients. The denaturation temperature was increased by incorporation of TG (6.53 - 8.33°C) and CG (6.42 - 8.33°C) but there was a decrease of enthalpy due to addition of TG (from 0.76 to –4.05 J/g) and CG (1.11 to –4.05 J/g). Only CG decreased the number of free amino acid groups (0.94 - 0.62) confirming that it catalysed the protein crosslinking of the oat glutelin while other ingredients increased it. Secondly, as CMC, YG and TG affected the mixing, pasting and thermal properties of oat dough, oat bread was baked with carboxylmethylcellulose (CMC), yoghurt (YG) and transglutaminase (TG) following a 33 Box-Behnken design consisting of CMC (1, 2 g), YG (10.75, 33.75 g) and TG (0.5, 1.5 g) as independent variables. The physical and textural analysis of oat bread showed that CMC, YG and TG addition did affect oat bread. TG decreased the springiness (6.47 - 4.14 mm), specific volume (1.61 - 1.54 ml/g) and increased hardness (537.85 - 692.41 N) of oat bread. No significant effect was observed on the colour parameters of crust and crumb of oat bread. Despite the optimal oat bread exhibited a high desirability, its high hardness and low springiness remain some challenges associated with oat bread production. Since it was well established that TG increased hardness and decreased springiness of the optimal oat bread, improvement was needed for the production of best oat bread. Thirdly, Psyllium husks (PH) and cyclodextrinase (CG) were added in five (05) best oat bread formulations such as (1) PH + CG, (2) CG, (3) TG + CG, (4) TG + PH and (5) TG + PH + CG. The best oat bread formulation with low hardness containing PH and CG was further used for sensory and shelf-life studies. The combination of ingredients psyllium husks and cyclodextrinase significantly (p < 0.05) improved the textural properties of best oat bread. It decreased the hardness (94.88 N) and increased the springiness (10.97 mm) of the best oat bread. Fourthly, the sensory evaluation showed that the consumers highly appreciated the crumb colour and texture of the best oat bread than the ones of wheat bread. In addition, they found that there was a strong correlation in crust and crumb colour between wheat and the best oat bread. However, some differences existed between the wheat and best oat bread. The best oat bread exhibited a less preference in taste than its wheat counterpart. The best oat bread positively received an overall acceptability (4.07) as wheat bread (4.22). Fively, the shelf-life studies of the best oat bread revealed that the pH and TVC of the best oat bread were more affected by the time, temperature and the interaction of both parameters (time and temperature) than Total Titratable Acidity (TTA), yeasts and mould as the storage time passed. The best oat bread could safely be stored up to 21 days at refrigeration temperature (5°C) with a Total Viable Count (TVC) load of 105 cfu/g. Finally, using survival analysis for the shelf-life studies of the best oat bread, the mathematical model revealed that the risk of deteriorating increased with the temperature.

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