Department of Food Science and Technology
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Item Antimicrobial Properties and Mechanism of Action of Some Plant Extracts Against Food Pathogens and Spoilage Microorganisms(Frontiers in Microbiology, 2018-07-24) Gonelimali, Faraja Deo; Jiheng, Lin; Wenhua, Miao; Jinghu, Xuan; Fedrick, Charles; Meiling, Chen; Shaimaa, Hatab RThis work aims to evaluate the antimicrobial potential of ethanolic and water extracts of roselle (Hibiscus sabdariffa), rosemary (Rosmarinus officinalis), clove (Syzygium aromaticum), and thyme (Thymus vulgaris) on some food pathogens and spoilage microorganisms. Agar well diffusion method has been used to determine the antimicrobial activities and minimum inhibitory concentrations (MIC) of different plant extracts against Gram-positive bacteria (Bacillus cereus, Staphylococcus aureus), Gram-negative bacteria (Escherichia coli, Salmonella enteritidis, Vibrio parahaemolyticus, and Pseudomonas aeruginosa), and one fungus (Candida albicans). The extracts exhibited both antibacterial and antifungal activities against tested microorganisms. Ethanolic roselle extract showed significant antibacterial activity (P < 0.05) against all tested bacterial strains, while no inhibitory effect on Candida albicans (CA) was observed. Only the ethanolic extracts of clove and thyme showed antifungal effects against CA with inhibition zones ranging from 25.2 ± 1.4 to 15.8 ± 1.2 mm, respectively. Bacillus cereus (BC) appears to be the most sensitive strain to the aqueous extract of clove with a MIC of 0.315%. To enhance our understanding of antimicrobial activity mechanism of plant extracts, the changes in internal pH (pHint), and membrane potential were measured in Staphylococcus aureus (SA) and Escherichia coli (EC) cells after exposure to the plant extracts. The results indicated that the plant extracts significantly affected the cell membrane of Gram-positive and Gram-negative bacteria, as demonstrated by the decline in pHint as well as cell membrane hyperpolarization. In conclusion, plant extracts are of great value as natural antimicrobials and can use safely as food preservativesItem Studies on the optimization of immobilising acetogenic and methanogenic biomass on polyurethane carrier(. Fac. Landbouw. Rijksuniv. Gent, 1989) Rubindamayugi, M.S.T.; Broeders, P.; op den Camp, H.J.M.; Lubberding, H.J.; Vogels, G.D.The influence of operational conditions (including the specific substrate concn in the feed, the hydraulic retention time and wastewater composition) on the rate of immobilization of acetogenic and methanogenic bacteria in an anaerobic polyurethane carrier reactor (PCR) treating synthetic Volatile Fatty Acids (VFA) based wastewater was investigated. The performance of continuous and fed batch culture reactor systems had a roughly similar start up period and biogas production rate. Preliminary results indicated that these systems started up within 8 d of operation. A max. concn of 151 mM acetate and 126 mM propionate was applied in the reactors treating VFA based wastewaters with a higher proportion of acetate and propionate, respectively. In all reactors a max. concn of 45.4 mM butyrate was applied. At max. acetate concn no toxic effect on acetogenic and methanogenic biomass activity were observed. The max. propionate concn showed strong inhibitory effect on biomass activity. At the max. feed concn the VFA conversion, methane production rate and methane content decreased. Biomass activiy tests showed that the reactors fed with a higher acetate concn showed higher acetogenic and methanogenic activity than the reactor treating wastewater with higher propionate concn. The influence of operational conditions on biomass washout were also investigated.Item The development of ice crystals in food products during the superchilling process and following storage, a review(Elsevier, 2014-10) Kaale, Lilian Daniel; Eikevik, Trygve MagneSuperchilling is a method of preserving food by partial ice crystallization. The ice stored in superchilled products will be used as a cold reservoir during distribution or storage. Chemical and physical changes such as low water holding capacity, increase in product drip loss may occur during superchilled storage. There is a need to study the factors which may influence on these changes. The information on the development of ice crystals during the superchilling process and following storage, which has a large influence on the quality of the final superchilled food, is useful for the industry in estimating the refrigeration requirements for a superchilling system and designing the necessary equipment.Item Physical properties of extruded snacks enriched with soybean and moringa leaf powder(International Research Journals, 2015-01) Rweyemamu, Leonard, M.P.; Yusuph, Athuman; Mrema, Godwill, D.This study was conducted to investigate the application of extrusion cooking in the production of snacks containing soybean (SB) and Moringa oleifera (MO) leaves as inexpensive sources of micronutrients. The specific objectives were to examine effects of barrel temperature, residence time and moisture content of feed on selected physical properties of extruded snacks (extrudates), namely water absorption index (WAI), water solubility index (WSI) and expansion ratio (ER). The extrudates were obtained by blending different levels of input ingredients of maize flour (MF) (55 to 80%), full fat soybean flour (FFSF) (10 to 30%), and Moringa oleifera leaf powder (MOLP) (5 to 15%). Extrusion process variables in a twin-screw extruder were at three levels for temperature (100, 130 and 160°C), feed moisture content (15, 22.5 and 30%), and residence time (60, 75 and 90 s). The performed study revealed that the level of incorporation of both FFSF and MOLP, and feed moisture content have significant effects on the expansion ratio, water solubility index and water absorption index of the extrudates. It was concluded that the role of processing conditions and blending levels have a significant contribution to the quality characteristics of the soy-moringa expanded snacks.