Food Science and Technology International

Nisin is a 34 amino acid antibacterial peptide produced by certain strains of Lactococcus lactis. This bacteriocin has found wide application as a food preservative owing to its non-toxic nature, its heat stability at acidic pH, its inactivation by proteolytic enzymes in the digestive tract and, especially, to its antimicrobial activity against a broad range of Gram-positive organisms, including food pathogens of concern in food industry such as Clostridium botulinum and Listeria monocytogenes. However, the use of nisin has the limitation that its solubility and stability decrease progressively as the environ mental pH increases. The two natural variants of nisin, named nisin A and nisin Z, are ribosomally synthesized as 57 amino acid precursor peptides which are subjected to further modifications. The mature peptide displays several unusual features, such as the presence of dehydrated amino acids and lanthionine rings. Insertion of the peptide into the cytoplasmic membrane of susceptible cells leads to the formation of pores, dissipating the membrane potential and pH gradients.

Protein denaturation during frozen storage at -18 "C for 16 weeks was studied in jack mackerel (Trachurus murphyi) actomyosin. The cryoprotective effect of different additives was evaluated at a level of 8°/, (w/w): sucrose/sorbitol (1:1), maltodextrin 25 DE, milk whey and sodium lactate. The results were compared with a control sample without additives. The decrease in protein solubility and calcium ATPase activity confirmed that protein denaturation occurred both during the freezing process and during frozen storage. Higher losses were observed after one week at -18 °C. Sucrose/sorbitol and maltodextrin 25 DE were the best cryoprotectants. DSC thermograms showed two endothermic transitions with T _max at 46.8 °C and 68.9 °C assigned to myosin and actin respectively. The best cryoprotective effect was achieved with sucrose/sorbitol and maltodextrin 25 DE. These additives showed T _max and ΔH values for myosin and actin significantly higher than the control.

Five vinifications were performed in 500 L tanks using two musts of the Malvar white grape variety. Four vinifications were carried out with or without the addition of sulphur dioxide by spontaneous fermentation and by a mixed culture of yeasts (Kloeckera apiculata, Torulaspora delbrueckii and Saccharomyces cerevisiae var ellipsoideus). A fifth experiment was performed with the addition of sulphur dioxide and the inoculation of a commercial active dry yeast (Saccharomyces cerevisiae 71 B). The decrease in amino acids during fermentation was similar in all the experiments carried out on the same must in which there was no malolactic fermentation, regardless of the species of yeast conducting the fermentation, the free amino acid content of the corresponding must or whether sulphur dioxide was added to the musts or not. There was a smaller decrease in free amino acid concentration in wines where malolactic fermentation took place. This could be related to the release of amino acids from the wines' peptides by the peptidase activity of lactic acid bacteria.

The seeds of different legumes (Lupinus albus var. Multolupa, Lens culinaris var. Magda 20, Cicer arietinum type Kabuli, Phaseolus vulgaris var. Guerniquesa, Vicia faba var. Alameda) were analysed for soyasaponin content and soyasapogenol composition using different chromatographic techniques. The soyasapogenol was present in all species, except in L. albus; the content ranged from 0.02 mg/g in V. faba var. Alameda to 1.21 mg/g in P. vulgaris var. Guerniquesa. Two soyasaponins were detected by FAB-MS. Soyasaponin I was detected in the L. culinaris, C. arietinum, V. faba and P. vulgaris extracts and soyasaponin V in the P. vulgaris extracts.

Non-enzymatic browning in an 11 "Brix apple juice during thermal treatment was studied through changes in colour by colorimetric parameters (A ₄₂₀, colour difference and index of browning), and HMF and sugars (fructose, glucose and sucrose) evolution. Zero and first order kinetics were applied to describe evolution of colorimetric parameters. The formation of HMF was fitted to auto- catalytical and first order equations. Sucrose tends to disappear according to a first order kinetics giving fructose and glucose. For the reducing sugars (fructose and glucose), no clear tendency was observed. The effect of temperature can be described by an Arrhenius-type equation.

This paper examines the gel-forming ability of minced muscle of sardine - caught from the Bay of Biscay and the Mediterranean at different seasons - kept in frozen storage for 150 days. The influence of atmospheric and vacuum packaging on the gel-forming capacity of minced muscle, and the addition of tocopherol as antyoxidant were also studied. From the outset of frozen storage, Mediterranean sardine muscle exhibited greater gel strength than that from the Bay of Biscay. Sardines from the Bay of Biscay caught in November produced the best gels from any area. Generally, when frozen muscle was vacuum-packed, rancidity was less and gel strength improved. Activity of tocopherol does not seem sufficiently clear. In nearly all cases, gel strength was greater the longer the muscle was kept in frozen storage, although in Bay of Biscay sardine muscle there was progressive myofibrillar protein aggregation throughout the storage.