Control of the bacteriological condition of calf brain. II. The effects of lactic acid decontamination and frozen storage

In two experiments the effects of lactic acid decontamination (LAD) and frozen storage on the bacteriological condition of calf brain were investigated. The first experiment incuded 80 calves, whose brains were extracted manually after splitting of the occipital bone with an axe. Upon removal, 40 brains were sprayed with 1.25% (v/v) L-lactic acid, whereas 40 brains remained untreated. At day 1 cone-shaped samples of 10 g were excised from 20 brains of each group at undamaged sites of the hemispheres and at the sites of impact of the captive bolt. After 7 days of storage at 3 ± 1°C in polystyrene trays the 20 remaining brains were sampled. The bacteriological examination included aerobic colony count at 30°C (ACC-30) and 4°C (ACC-4), mesophilic Enterobacteriaceae colony count (EC-37) and Lancefield group D streptococci colony count. For both locations and with regard to all parameters examined LAD resulted in significantly lower bacterial counts at day 1 as compared with controls. However, the differences were slight particularly at the damaged locations where a reduction in ACC-30 and ACC-4 of only 0.3 log g^?1 was effected. At day 8, bacterial counts were no longer significantly different, with the exception of ACC-4 at the site of impact of the captive bolt, which was 7.0 log g^?1 and 7.5 log g^?1 for treated and control brain respectively. Moreover, treated brain exhibited an unacceptable discolouration. From these findings it was concluded that lactic acid decontamination does not give an appreciable extension of the storage life of calf brain. The second experiment involved aseptically removed brains of 20 mechanically stunned calves. Ten brains were sampled at day 1, whereas brains of 10 other calves were stored at ?40°C for 7 days. Subsequent they were allowed to thaw for 1 day at 3 ± 1°C. At day 9 these brains had bacterial counts similar to those obtained at day 1. Thawing loss was somewhat higher (5.1%) than the weight loss of cooler-stored controls stored at 3 ± 1°C (1.2%). It is concluded that in view of the susceptibility of calf brain to bacterial spoilage, freezing should be taken into consideration as an effective means to prevent growth of bacteria that will lead to deterioration.