Trevor J. Britz

Impact of freezing and thawing on the quality of meat: Review

This comprehensive review describes the effects of freezing and thawing on the physical quality parameters of meat. The formation of ice crystals during freezing damages the ultrastructure and concentrates the solutes in the meat which, in turn, leads to alterations in the biochemical reactions that occur at the cellular level and influence the physical quality parameters of the meat. The quality parameters that were evaluated are moisture loss, protein denaturation, lipid and protein oxidation, colour, pH, shear force and microbial spoilage. Additionally mechanisms employed to mitigate the effects of freezing and thawing were also reviewed. These include the use of novel methods of freezing and thawing, ante and post mortem antifreeze protein inclusion and vitamin E supplementation, brine injection and modified atmospheric packaging.

Meat quality comparison between fresh and frozen/thawed ostrich M. iliofibularis

A pairwise comparison of the meat quality between fresh and frozen/thawed Musculus iliofibularis was conducted. Thirty-two (16 left; 16 right) muscles were collected and allocated to two treatments: fresh and frozen/thawed. Frozen vacuum-packed samples were stored for 1 month at -20°C before thawing. The fresh samples had higher pH (P<0.05), water binding capacity (P<0.05), CIE L* (P<0.0001), CIE a* (P<0.05) and Chroma values (P<0.05) than the frozen/thawed samples, indicating the fresh samples were bright red in appearance and had minimal exudate. The frozen/thawed samples lost 5.09±0.21% moisture during thawing and had a greater drip loss (P<0.0001) and shear force (P<0.001). No differences were obtained with regard to cooking loss, CIE b*, hue and TBARS. Protein oxidation (mM carbonyls/mg protein) was lower (P<0.05) in the frozen/thawed samples, which was attributed to the higher (P<0.0001) protein concentration negating the higher (P<0.001) carbonyl content. Industrial freezing and thawing regimes negatively affected the quality of ostrich meat.

Anaerobic digestion of baker's yeast factory effluent using an anaerobic filter and a hybrid digester

Abstract A high-strength effluent from a bakers yeast factory was treated using a hybrid and an anaerobic filter digester under mesophilic conditions. The effluent COD composition varied considerably (11000–88000 mg liter−1) and contained high sulfate concentrations. The digesters were subjected to quantitative increases in organic loading rate (OLR; 1·8–10·0 kg COD m−3 day−1) at a set hydraulic retention time of 3·0 days. The data showed that the anaerobic digestion process is feasible for the treatment of, and methane generation from, bakers yeast factory effluent without pretreatment. The results obtained showed that, in general, the two digester designs reacted in a similar manner to increases in OLR. A COD removal efficiency and methane yield of 67% and 0·207 m3 kg−1 CODremoved for the anaerobic filter and 65% and 0·208 m3 kg−1 CODremoved for the hybrid, respectively, could be achieved at an OLR of 8·6 kg COD m−3 day−1. The data also showed that both digesters could be maintained at a hydraulic retention time of 3·0 day with an OLR of 10·0 kg COD m−3 day−1. Decreasing digester efficiency was characterized by accumulation of iso-butyric and propionic acids.

Physical meat quality characteristics of hot-deboned ostrich (Struthio camelus var. domesticus) Muscularis gastrocnemius, pars interna during post-mortem aging

There is a risk of shortening and toughening with hot-deboning of muscles. However, with refrigerated aging this phenomenon may be negated. Vacuum-packed hot and cold-deboned ostrich Muscularis gastrocnemius, pars interna were stored for 21 d at 4°C to investigate the effects of hot-deboning on quality characteristics of ostrich meat during refrigerated storage. Muscle pH did not differ (P>0.05) between hot and cold-deboned muscles during storage. Hot-deboning caused (P<0.0001) more purge in the vacuum packages of the hot-deboned muscles (1.83±1.31%) than in the cold-deboned muscles (0.67±075%) during the 21-d aging period. Hot-deboned muscles were tougher (P<0.05) than cold-deboned muscles from 24h up to 5 d. Although hot-deboning caused muscles to be tougher than cold-deboned muscles, with aging at 4°C beyond 5 d this toughness was found to be insignificant.

ANAEROBIC TREATMENT OF BAKER'S YEAST EFFLUENT USING A HYBRID DIGESTER WITH POLYURETHANE AS SUPPORT MATERIAL

SummaryA high-strength bakers yeast effluent was anaerobically treated using a hybrid digester under mesophilic conditions. The digester was subjected to a substrate COD concentration of 21 767 mg/I at three different HRTs. At HRTs of 3.0, 2.0 and 1.0 d, the digester reduced the substrate COD by 76, 61 and 33%, respectively. Although the best COD removal was obtained at an OLR of 7.30 kg COD/m3.d, the highest COD removal rate (6.51 kg COD/M3-d) was found at 10.65 kg COD/m3.d at an HRT of 2.0 d. The low methane yield and VFA accumulation found in the digester effluent, indicated inhibition on methanogenic level and this was considered to be the rate-limiting step during the anaerobic treatment process. The overall efficiency of the digester indicated that this digester design and support medium was suitable for the treatment of a high-strength, sulfate-rich bakers yeast effluent.

Influence of phenol additions on the efficiency of an anaerobic hybrid digester treating landfill leachate

SummaryA hybrid digester with leachate as substrate was used to determine the influence of the addition of phenol. The phenol was increased stepwise from 2 to 25 mg/l and then to 30, 40, 50 and 60 mg/l leachate. Within 24 h the addition caused a significant decrease in the COD removal and biogas production while the methane content increased. Phenol loading was characterised by the accumulation of volatile fatty acids. With the continuous addition of phenol, a recovery time of 28 d was required for the performance to reach the control values. As the concentration was increased, the recovery time shortened to 8 d at 20 mg/l. At higher concentrations (>50 mg/l) the recovery time was found to increase to >60 d.

Muscle pH and temperature changes in hot- and cold-deboned ostrich (Struthio camelus var. domesticus) Muscularis gastrocnemius, pars interna and Muscularis iliofibularis during the first 23 h post-mortem

Cold-shortening is the response when muscles are exposed to temperatures below 10°C with a pH>6.20. The course of pH within hot-deboned and intact ostrich M. gastrocnemius, pars interna and M. iliofibularis were followed for the first 23-24h post-mortem to investigate the changes in pH as well as to determine the point of minimum pH for ostrich muscles post-mortem. The hot-deboned muscles took longer to reach the point of minimum pH than the intact muscles. There was no significant (P=0.4508) difference in the minimum pH (5.91±0.26) between the hot-deboned and the intact muscles. It was concluded that both the M. gastrocnemius, pars interna and the M. iliofibularis reached a pH<6.20 early post-mortem with muscle temperatures above 10°C; and therefore showed no risk of cold-shortening if these muscles were to be hot-deboned 2-4h post-mortem.

Microbial content of commercial South African high-moisture dried fruits

Aim:  The aim was to evaluate commercially available South African high‐moisture dried fruits (HMDF) for the microbial, moisture and SO2 contents, as well as aw and pH.

Evaluation of different preservation techniques on the storage potential of Kefir grains

Kefir is an acidic, mildly alcoholic dairy beverage produced by the fermentation of milk with a grain-like starter culture (Koroleva, 1988). These grains usually contain a relatively stable and specific balance of microbes that exist in a complex symbiotic relationship (Obermann & Libudzisz, 1998; Witthuhn et al. 2004). The different groups of microbes present in the grains are active at different stages of the fermentation (Koroleva, 1982). The lactococci, including Lactococcus lactis subsp. lactis, Lc. lactis subsp. cremoris and Lc. lactis subsp. diacetilactis provide rapid acid development during the first hours of the fermentation (Litopoulou-Tzanetaki & Tzanetakis, 2000). As the acidity of the milk increases it provides favourable conditions for the growth of the lactobacilli (Rea et al. 1996). The yeasts, acetic acid bacteria and the aroma-producing microbes, mainly leuconostocs, have a much slower growth rate than the lactic acid producers, resulting in the slow production of the aroma compounds and the gradual increase in the concentration of these substances in the later stages of the fermentation (Koroleva, 1982). In the past the preservation of the microbial populations present in the traditional Kefir grains was achieved by methods including freezing (Garrote et al. 1997), lyophilisation (Oberman & Libudzisz, 1998), air-drying (Kroger, 1993) and refrigeration (Marshall, 1993). Research has shown that traditional Kefir grains preserved by air-drying and lyophilisation retain their activity for up to 12-18 months (Oberman & Libudzisz, 1998). Frozen grains stored at -20 degrees C were found to maintain the microbial activity for up to 7-8 months, whereas grains stored at refrigerated temperatures showed a decreased activity after about 10 d (Oberman & Libudzisz, 1998). The aim of this study was to evaluate the impact of four different preservation techniques on the activity of mass cultured Kefir grains (Schoevers & Britz, 2003). The activity of the grains was evaluated at different time intervals using four activity measurements, including changes in substrate pH, titratable acidity (TA), lactose and lactic acid levels of the final Kefir beverage.

Identification of microbial contaminants present during the curing of honeybush tea (Cyclopia)

Honeybush tea (Cyclopia) is produced over a wide area ofthe Western and Eastern Provinces of South Africa and exported to several countries worldwide. It is traditionally manufactured by curing honeybush material for several days at relatively high temperatures and moisture contents and this results in extensive mould and bacterial growth. This leads to a product with inferior leaf colour and organoleptic quality as well as health concerns. Unlike during the manufacture of black tea, honeybush curing temperatures do not reach levels where these contaminants are eliminated. The microbial contaminants and the minimum temperatures necessary to eliminate these organisms were thus investigated. Yeast-Glucose (YG), Yeast-Starch (YpSs) and Czapek media were evaluated for the isolation of contaminants that developed during the curing of honeybush tea. YG and YpSs gave good results, while the Czapek medium was found to be unsatisfactory for the detection of microbial contaminants. A low pH (pH 5.0) favoured mould growth, while bacteria proliferated at pH 7.0. Honeybush material fermented in a curing heap and material fermented under controlled conditions at 40 and 50°C showed microbial contamination, but no contaminants were detected on or in material fermented at higher temperatures (60, 70 and 80°C). Two thermophilic moulds, Humicola grisea var thermoida and Humicola lanuginosa, a thermotolerant mould, Rhizomucor pusillus, and five endospore-forming species of the genus Bacillus were isolated. The data indicated that R pusillus was the predominant microbial contaminant.