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Summary The effect of stratification in ice on the quality of fresh water prawns was monitored by microbiological, subjective and objective textural analyses. In general, prawns in the lower layers of ice exhibited more marked textural changes and greater numbers of potential spoilage bacteria were found on them. No connection was found between the number of proteolytic bacteria and textural changes in the prawn muscle.

Summary The effects of short heat (boiling temperature) treatments, consisting of ‘blanching’ in concentrated sucrose (70%) solution (I), or plain water (11); or osmotic dehydration in cold (room temperature) (111) or hot (boiling) sucrose (70%) solution (IV); and a combination of (111) following (I) or (11), on the drying behaviour of papaya, dehydrated to the intermediate moisture (IM) range, were studied. Significant increases were observed in the dry matter content of papaya treated as above (I, 111, IV or 111 following T or IT), with the obvious increase in the expected production yields and probable reduction of the heat energy needed for the drying process. The drying behaviour of papaya as a raw material for IM products, during and after the above treatments, as well as following hot-air, (cabinet) or direct-sun drying, was studied. The drying time needed for cabinet or solar drying following osmotic treatments of papaya was considerably shortened, and therefore a significant saving in the heat energy needed for drying is to be expected. The optimal treatments to achieve a considerable shortening in the drying time, without affecting negatively the quality of the 1M papaya, seemed to be syrup ‘dipping’, or a combination of water or syrup blanching and cold osmotic dehydration. The above methods can be applied in both small, non-sophisticated fruit dehydration plants (mainly solar drying), or in larger and more sophisticated ones (mainly forced hot-air drying).

Summary The shelf life of fresh water prawns stored at 0°C was judged by a sensory panel and monitored by microbiological and chemical tests. After 14 days’ storage, but not after only 10 days, frozen (control sample) prawns were preferred over the former. During this period too, TVBN values of 0°C-stored prawn tails rose from 22 to 31 mg per 100 g, and TBA values rose from 0.25 to 0.65; the total aerobic psychrotrophic plate counts increased by about 2 logarithmic units. The relationship between the results of the various tests is discussed.

Summary The viable counts of total aerobic mesophiles and psychrophiles, coliforms, coagulase-positive staphylococci and salmonellae in green beans were greatly reduced by blanching in the course of their preparation for freezing. The increase in bactcrial numbers between blanching and freezing appears to be caused by contamination from the conveyor belt and from the hands of employees. Salmonellae, detected in small numbers prior to blanching, were not recovered after blanching. Freezing at a rate of 4–5°C per min, had only a slight destructive effect on the various bacterial groups studied. A significant reduction in counts, especially of coliforms and staphylococci, occurred after 4 weeks of frozen storage. Aerobacter aerogenes was the main coliform organism recovered from the frozen green beans.

The effect of gamma radiation on the quality characteristics o f pomegranate kernels stored in plastic pouches at refrigerator temperatures was studied. Irradiation at doses of 0.2 and 0.4 Mrad markedly reduced the load of potential spoilage microorganisms. Fungal contaminants exhibited much higher radiation resistance than bacterial contaminants, which were eradicated at 0.4 Mrad. The predominant fungus isolated from non-irradiated pomegranate kernels was Penicillium frequentans while after irradiation at all doses tested kernels yielded the fungus Sporofhrix cyanescens. An adverse effect of irradiation on colour was observed. The results of a taste evaluation panel did not indicate a significant difference between irradiated and control samples. lt is concluded that the feasibility of irradiation for prolonging the storage life of packaged pomegranate kernels is questionable.

Summary Freezing (- 40°C) a cell suspension of Salmonella gallinarum at a cooling rate of 18°C per min and an initial cell concentration of 37 × 107 cells/ml resulted in a recovery more than five times that obtained from a lower cooling rate (0.5°C per min). Decreasing the initial cell concentration to 12 × 103 cells/ml at the higher cooling rate resulted in an increase of only twice the recovery of the lower rate. The percentage recovery from the higher cell concentration was greater than from the lower concentration, only at the higher cooling rate. The apparent recovery of Salmonella gallinarum on a selective medium immediately after freezing, was only 60% of that on a nonselective medium, and decreased to 5% after 1 week of storage at - 20°C.

In response to environmental stress, the p53 phosphoprotein is stabilized and activated to inhibit cell growth. p53 stability and activity are negatively regulated by the murine double minute (Mdm2) oncoprotein in an autoregulatory feedback loop. The inhibitory effect of Mdm2 on p53 has to be tightly regulated for proper p53 activity. Phosphorylation is an important level of p53 regulation. In response to DNA damage, p53 is phosphorylated at several N-terminal serines. In this study we examined the role of Ser20, a potential phosphorylation site in human p53, in the regulation of p53 stability and function. Substitution of Ser20 by Ala (p53-Ala20) significantly increases the susceptibility of human p53 to negative regulation by Mdm2 in vivo, as measured by apoptosis and transcription activation assays. Mutation of Ser20 to Ala renders p53 less stable and more prone to Mdm2-mediated degradation. While the in vitro binding of p53 to Mdm2 is not increased by the Ala20 mutation, the same mutation results in a markedly enhanced binding in vivo. This is consistent with the conclusion that phosphorylation of Ser20 in vivo attenuates the binding of wild-type p53 to Mdm2. Peptides bearing non-phosphorylated Ser20 or Ala20 compete with p53 for Mdm2 binding, while a similar peptide with phosphorylated Ser20 does not. This implies a critical role for Ser20 in modulating the negative regulation of p53 by Mdm2, probably through phosphorylation-dependent inhibition of p53-Mdm2 interaction.

The l-anilino-8-naphthalenesulphonic acid (ANS) fluorescent probe was used to monitor alterations in the cytoplasmic membrane of sensitive Lactobacillus plantarurm cells, caused by pediocin SJ-1, a bacteriocin produced by Pediococcus acidilactici. The addition of pediocin SJ-1 to the sensitive cells caused an increase in fluorescence intensity of ANS and a blue shift in its emission maximum from 520 to 475 nm. None of these spectral changes could be detected when pediocin SJ-1 was added to cells of a Lact. plantarum variant resistant to pediocin SJ-1. Upon the addition of pediocin SJ-1, dose-dependent energy transfer took place between tryptophanyl residues in the cytoplasmic membrane of sensitive cells and ANS. Similar ANS-fluorescence changes were observed with the bacteriocin nisin. The concentrations of pediocin SJ-1 needed to effect changes in the fluorescence spectrum of ANS were of the same magnitude as those required for a bactericidal effect and the release of u.v.-absorbing material. A hypothesis on the mode of action of pediocin SJ-1 is proposed.

A strain of Leuconostoc mesenteroides that was able to reduce the viscosity of tomato juice serum and of a growth medium containing pectin was isolated and the pectolytic activity of its cell-free culture supernatant (CFS) was studied. In vitro tests showed that the CFS was active on high methoxyl pectin but almost inactive on low methoxyl pectin and polygalacturonic acid. It was most active in the pH range 4mD5–5mD5 and had no detectable pectinesterase activity. In vivo tests showed that the CFS degraded pectin in the walls of tomato fruit cells and caused degradation of cucumber fruit tissues.

Ascorbic acid (AsA), added to nutrient broth at a concentration of 5 mmol/l, was bactericidal towards Campylobacter jejuni grown at 42 degrees C in a micro-aerobic atmosphere. Specific enzymes, radical scavengers, metal chelators and reducing agents were tested as possible antagonists to the cytotoxicity of AsA. The addition of catalase or of the metal chelators ceruloplasmin or Desferal did not prevent the cytotoxic effect of AsA. The addition of the hydroxyl radical scavengers mannitol, formate, histidine or DMSO also failed to counteract the toxicity of AsA. On the other hand, thiourea or cysteamine and the reducing agents cysteine or dithionite significantly increased the recovery of C. jejuni in the presence of AsA. Although the possibility of the involvement of hydroxyl radicals in AsA cytotoxicity cannot be ruled out, it appears that the toxic effect of AsA is due mostly to the formation of products of oxidation of AsA and particularly to dehydroascorbic acid (DHA). Dehydroascorbic acid was also bactericidal to C. jejuni at a concentration of 5 mmol/l. Of all the compounds tested, only cysteamine was effective in preventing (partially) the toxic effect of DHA. The growth of C. jejuni was not inhibited by the addition of 5 mmol/l of isoascorbic acid or sodium isoascorbate.

Exposure of a nutrient agar medium to the combined action of fluorescent light and air produced toxic factors in the medium which affected the growth of Campylobacter jejuni. Sodium dithionite (5-10 mM), a powerful reducing agent, and catalase were effective in counteracting the injurious action of light and air. Among the quenchers of singlet oxygen tested, only histidine had a beneficial effect on the recovery of C. jejuni in the photo-oxidized medium, while the addition of superoxide dismutase, a hydroxyl radical scavenger such as cysteamine, or the free radical antioxidants tocopherol and butylated hydroxy toluene, did not increase the recovery rate of photochemically injured cells. Histidine (40 mM) and dithionite (5-10 mM) also assisted recovery of C. jejuni inoculated on nutrient agar stored in air in the dark. Cysteamine and dithionite were toxic to Campylobacter when added at concentrations of greater than or equal to 10 mM and greater than or equal to 20 mM, respectively. A high inoculum of C. jejuni could not be recovered in unsupplemented nutrient agar incubated in air but was recovered in atmospheres containing 17 or 21% oxygen plus 10% carbon dioxide. The addition of dithionite, catalase or histidine resulted some colony formation on nutrient agar incubated in air. Among the scavengers tested, only dithionite was consistently able to maintain the viability of C. jejuni on nutrient agar stored in air for longer than 4 weeks. In view of the ability of catalase, dithionite and histidine to enhance the aerotolerance of C. jejuni, it is concluded that various oxygen species might be involved in the toxicity of high levels of oxygen.

The effects of S-nitrosocysteine (RSNO) as an inhibitor of lipid oxidation and as a color-developing and anticlostridial agent in a comminuted turkey meat product are reported. These effects were compared with those of nitrite on a molecular weight basis. Similar effects were obtained by 25 ppm of nitrite or the corresponding molar concentration of RSNO in color development and inhibition of lipid oxidation in cooked cured meat stored under anaerobic conditions. Transnitrosation between RSNO and hemeproteins occurred in the meat product. Results indicate that as far as the chances for nitrosamines formation are concerned, RSNO cannot be recommended as a substitute for nitrite. In a microbiological medium and in a meat product, RSNO had less anticlostridial activity than nitrite.

Summary Salmonella gallinarum suspended in distilled water was frozen at a rate of 22°C/min, 86% of the cells were inactivated, as determined from differences in numbers of colony-forming units observed on TSA medium before and after freezing. About 35% of the viable survivors were injured, as determined by their failure to form colonies on a minimal plating medium (MA) but their success on a ‘complete’ medium (TSA). Following 1 hr incubation of the frozen-thawed cells in water or in 0.3 mM monopotassium phosphate, the percentage survival was reduced from 14 to 8% whereas in selenite cystine or tetrathionate broths, the percentage of survivors was reduced to about 3%. Higher recoveries of the frozen-thawed cells were obtained when nonselective suspending media such as nutrient broth and lactose broth were employed. The possibility of obtaining better recovery by the addition of specific compounds to plating media was investigated. Filter-sterilized catalase or vitamin-free hydrolyzed casein, when added to the minimal agar medium improved the recovery of frozen-thawed S. gallinarum by 32 and 34% respectively. Sodium pyruvate, heat-sterilized catalase or ethylenediaminetetraacetic acid had no significant effect, but the addition of haemin or cysteine reduced the rate of recovery by 48 and 57% respectively.

Twelve strains of meat lactic starter cultures (Pediococcus spp. and Lactobacillus plantarum) were found to produce hydrogen peroxide in vitro. The (cumulative) amounts of H2O2 produced were measured through the peroxidative action of catalase on H2O2 and oxidation of added formate to CO2 by the H2O2-catalase complex formed. There was a problem in building a calibration curve for converting values of formate oxidation into amounts of H2O2, either by adding H2O2 directly to the assay mixture or having it produced via a glucose-glucose oxidase system.

The increased heat resistance of yeasts in orange concentrates as compared with single-strength juices cannot be accounted for on the basis of sugar contents only. Citric acid is demonstrated to play a role in the heat resistance of spoilage yeasts in concentrated orange juices. Other major chemical constituents of citrus juices, namely, ascorbic acid and pectin, did not exhibit any significant effect. A model system, based on sucrose, glucose, fructose, citric acid and tripotassium citrate, is pro-posed for the evaluation of the thermal resistance of yeasts in citrus concentrates.

Poly (hexamethylene biguanide hydrochloride) (PHMB), an industrial disinfectant, was evaluated for potential use in the food industry following suggestions in the literature. A colorimetric test based on the reaction with nitro-prusside reagent was found suitable for the dosimetry of this compound. In a bacteriological medium, at a concentration of 20 μg/ml, PHMB was inhibitory to Escherichia coli, less effective against Staphylococcus aureus, and practically ineffective against Pseudomonas aeruginosa. The bactericidal activity of PHMB was impaired in the presence of milk but little affected upon the addition of blood. Finally, in a toxicological test in vitro, PHMB was found to be toxic toward Chinese hamster cells, at doses similar to those required for antibacterial activity.

Summary. Treatment of green olives for 2 min with dilute hot alkali before brining increased the release of sugars, B complex vitamins, amino acids and phenolic compounds, and enhanced the establishment of lactic acid bacteria in the brine. Two components of the ethyl acetate extract of green olives, which showed an antibacterial activity, were isolated and identified as the glycoside oleuropein and its phenolic aglycone. The inhibition of Lactobacillus plantarum by the ethyl acetate extract or by oleuropein was augmented by reducing the concentration of organic nitrogenous compounds, increasing the NaCl concentration in the assay medium and decreasing the inoculum size. Besides its activity towards various bacteria, oleuropein inhibited the growth of Geotrichum candidum Link, Rhizopus sp. and Rhizoctonia solani Kuhn. On the basis of these findings, an explanation for some problems in the lactic fermentation of green olives is suggested.

SUMMARY The marked enhancement of lactic fermentation rates of intact Merhavia and Manzanillo green olives in brine following pretreatment with hot alkali results mainly from the destruction of an antilactic factor by the alkali. The press juice of Manzanillo green olives contains an ether-extractable, hot alkali labile factor which temporarily inhibits acid production by Lactobacillus plantarum in APT broth. A rapid method for the detection of the antilactic factor is described. The antilactic factor present in intact green olives may not be the same as that in the press juice.

In an attempt to use specific bacterial metabolites in a monitoring system to detect initial signs of spoilage of tomato products, the changes in bacterial counts, pH, titratable acidity and the accumulation of lactic acid, hydrogen peroxide, diacetyl (DA) and acetoin (AMC) in tomato juices inoculated with Lactobacillus plantarum, L. fermentum and Leuconostoc mesenteroides, were studied. Of the metabolites tested, it appears that DA and AMC can be taken as valuable indicators of contamination of tomato juice by lactic acid bacteria at early stages but not at advanced stages of bacterial growth.

Strains of Lactobacillus sp., Leuconostoc sp. and Streptococcus sp. were preserved for 6–24 months at ambient temperature, partially dehydrated on granular pumice stone. To date, all the cultures stored by this technique have remained viable and no changes in the cultural or biochemical characteristics were observed.