Spoilage yeasts.

Yeasts are best known for their beneficial contributions to society, and the literature abounds with discussions of their role in the fermentation of alcoholic beverages, bread, and other products. Yeasts also cause spoilage, but, with a few exceptions, this unwanted activity often goes unrecognized and underestimated as a major problem in the food and beverage industries. In some cases, there is only a fine line between what is perceived as either a spoilage or beneficial activity. This review examines the occurrence and growth of yeasts in foods and beverages with respect to their spoilage activities, the biochemistry of this spoilage, and technologies for the enumeration and identification of spoilage yeasts.     

Bacteriology of Spoilage of Fish Muscle: II. Incidence of Spoilers During Spoilage1

A test medium consisting of a sterile raw press juice from fish muscle was used to determine the incidence of spoilage bacteria on stored fillets of English sole (Parophrys vetulus). The initial load of spoilers was shown to be consistently below 10%. This percentage rose but slightly toward the middle of the spoilage runs, and actually declined when spoilage was most apparent both organoleptically and chemically. Further evidence implicating the Pseudomonas and Achromobacter groups in the spoilage of fresh fish is presented.     

Spoilage association of chicken skin.

The bacterial succession on the skin of broiler chicken carcasses stored at 2 degrees C was traced, and the ability of representative isolates to produce off-odors was determined by using sterile leg and breast muscle sections. Off-odors were identified by olfactory and chemical means. The inability of peptone-iron agar to detect sulfide-producing strains was noted.     

Spoilage association of chicken skin.

The bacterial succession on the skin of broiler chicken carcasses stored at 2 degrees C was traced, and the ability of representative isolates to produce off-odors was determined by using sterile leg and breast muscle sections. Off-odors were identified by olfactory and chemical means. The inability of peptone-iron agar to detect sulfide-producing strains was noted.     

Bacterial Spoilage of Thawed Frozen Peas

The main groups of bacteria developing in peas were isolated on differential media. Leuconostoc mesenteroides and Streptococcus lactis predominated and smaller numbers of catalase positive 'coryneform'bacteria were also regularly present. Strep. cremoris , streptococci (group D), catalase positive cocci and Gram negative rods were less regularly isolated.
Bacterial spoilage of untreated peas was usually accompanied by the development of a yellow colour and a reduction in pH. In pure culture in peas leuconostocs and group N streptococci produced an acid pH while the catalase positive organisms produced alkali, sometimes with ammoniacal odours. In mixed cultures in peas the products of a leuconostoc and a 'coryneform'tended to neutralize each other. A leuconostoc and a 'coryneform'did not interfere with each others'growth when grown from similar inocula. The behaviour of streptococci is still being investigated. The type and rate of spoilage probably depends on the balance between ammonia production and acid production in the system.     

Microbial Spoilage of Fresh Refrigerated Beef Liver

The types and numbers of micro-organisms involved in the spoilage of refrigerated beef liver were studied together with pH, hydration and organoleptic changes of the material. Fresh liver harboured a mixed population ( c . 1 × 10⁵ organisms/g) of Gram positive cocci, chromogens and non-chromogens, sporeformers, presumptive coliforms and Gram negative rods. When samples were rejected organoleptically, after 7–10 days at 5°, the contamination attained levels of c . 7–8 × 10⁷ organisms/g. Spoilage was due to souring; the pH fell from 6·3 (fresh liver) to c . 5·9. Lactic acid bacteria were predominant and Gram negative bacteria did not exceed 1·0 × 10⁶ organisms/g. This type of spoilage is explained by the carbohydrate content of c . 5% in liver. The value of pH appears to be a reliable indicator of liver freshness, with a pH of 6·1 indicating incipient spoilage.     

Lactobacilli Causing Spoilage of Acetic Acid Preserves

Twentyseven cultures of lactobacilli, isolated from 27 packs of spoiled vinegar preserves, which originated from 21 manufacturers and included 12 varieties of product, were examined according to the system of Rogosa & Sharpe and by other tests. One culture conformed to the characteristics of Lactobacillus casei var. casei ; 2 cultures to those of L. brevis ; 4 cultures to those of L. buchneri ; and 20 to those of L. fructivorans. On the basis of the results and an examination of the literature it is suggested that L. trichodes is a synonym of L. fructivorans.     

Spoilage association of chicken leg muscle.

The ability of pure cultures of bacteria isolated from spoiling chicken leg muscle to produce strong off-odors was tested by using sterile leg muscle sections. Changes in the flora during storage and the incidence and identity of organisms capable of producing strong off-odors were noted.     

Extracellular Enzymic Activity of Poultry Spoilage Bacteria

The extracellular enzymic activity has been studied of 224 strains of bacteria isolated mainly at 1° from spoiling chickens and turkeys and from poultry processing plants. The isolates comprised 44 strains of pigmented Pseudomonas , 57 strains of nonpigmented Pseudomonas , 29 strains of Ps. putrefaciens , 50 strains of oxidase positive Acinetobacter and 44 strains of oxidase negative Acinetobacter. None of the strains showed any significant activity against dextrin, starch, glycogen, inulin, dextran, xylan or pectin. Proteolytic activity was found mainly amongst 2 groups of pigmented pseudo-monads, and Ps. putrefaciens. Nuclease activity was found particularly amongst strains of Ps. putrefaciens and the oxidase negative Acinetobacter strains isolated from spoiling poultry. Almost all of the strains showed lipolytic activity when tested with tributyrin and a proportion of strains could also attack chicken fat. This latter property was particularly evident amongst the nonpigmented Pseudomonas strains.     

工业杀菌剂的抗性研究

<正>现代工业的迅速发展对工业材料的性质和功能不断提出更高的要求,工业杀菌剂的适用领域已经从纺织、木材、纸张、石油制品、胶黏剂、涂料等一直扩大到塑料、玻璃、陶瓷金属乃至航天部件等,工业中几     

Susceptibility of Strawberry Varieties to Post-harvest Fungal Spoilage

The susceptibility of strawberry fruits from eleven varieties, Cambridge Favourite, Cambridge Vigour, Cambridge Prizewinner, Red Gauntlet, Chanil, Domanil, Grandee, Litessa, Tamella. Senga Gigana and Precosana, to post-harvest spoilage fungi was investigated over the 1974 and 1975 seasons. Although the fruit from the different varieties from each of two sites at each harvest was contaminated with a similar level of fungi, the pattern of development of the spoilage fungi revealed marked differences between some varieties. Botrytis cinerea and Mucor mucedo were the predominant spoilage fungi on all varieties with Rhizopus sexualis and R. stolonifer being of minor importance. The relative importance of these fungi changed on all varieties as the season progressed, although to a different degree according to variety, site and season. Cambridge Vigour, Senga Gigana, and Chanil were the most susceptible varieties, while Red Gauntlet was the most resistant, especially to the Phycomycetes.     

Spoilage of stored cotton fibre from Sudan Gezira

Washings from long staple cotton (Gossypium barbadense L.) new variety Barakat, yielded Aspergillus flavus, A. nidulans, A niger. A. terreus, A. versicolor and Cladosporium herbarum. The number of propagules increased with R. H. following 6 month-storage. A. terreus was less favoured.Higher R. H. impaired fibre length and strength of both raw non-sterilized and inoculated sterile lint whilst the sterilized non-inoculated control was insignificantly affected, even at 100% R.H. Artificial inoculation of lint with Chaetomium globosum and A. nidulans significantly affected the efficiency of yarn spinnability at 80, 90 and 100% R.H. (P=0.05).Hyphae, which wound in a helical pattern around the fibre, intermittently dissolved fibre wall causing fibre fragility.