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.

Call number: LD2668 .T4 1986 X79 / Master of Science / Grain Science and Industry

Call number: LD2668 .T4 1985 C64 / Master of Science

In this research, three alternative approaches to chemical preservatives to extend the mold free shelf-life and quality of pita bread were investigated namely: Modified Atmosphere Packaging (MAP) involving gas packaging, oxygen absorbents technology and ethanol vapor generators, high pressures, and direct and indirect heating. / Gas packaging using 60%CO2 (balance N2) inhibited the growth of Aspergillus niger and Penicillium notatum from 3d (pita bread packaged in air) to 35d at ambient temperature. A longer extension in shelf-life (42d) was possible using an Ageless oxygen absorbent or a Freshmax oxygen absorbent label in conjunction with gas packaging. / Similar results were obtained with 2G--4G sachets of Ethicap, and 100--200S sachets of Negamold, a dual functional oxygen absorbent-ethanol vapor generator. / High pressures (30--400MPa) used to inhibit mold growth, resulted in delamination of the packaging film and textural changes to the pita bread. / Other alternatives, such as direct heating and microwave processing had a minimal effect in increasing the shelf-life of pita bread. (Abstract shortened by UMI.)

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