Preparation and molecular characterization of chitosans obtained from shrimp (Litopenaeus vannamei) shells.

Four chitosan samples were prepared from shrimp shells without deproteination and decoloration steps, by a deacetylation process at 2 reaction times (2 and 4 h) and with/without using a reducing agent (R.A.). Variations in the physicochemical properties of the final products were analyzed. Viscosity average molecular weight (Mw) determinations demonstrated the protective action of the R.A. on the molecular oxidative degradation. Oppositely, an increase on the reaction time produced samples with low Mw. Deacetylation degrees (DDs) were chemically evaluated by the nitrogen content and by spectroscopic techniques as infrared and nuclear magnetic resonance. The existing differences in crystallinity were studied by X-ray diffraction. Differential scanning calorimetry and thermogravimetry were used to demonstrate the dehydration and thermal degradation processes of the different chitosans. A novel method from calorimetric profiles is presenting for DD determinations of chitosan, which achieved highly satisfactory results (linear fit and Pearson's correlation coefficient) and is proposed to be generally extended to complex curves application.

Frozen storage of dressed and pre-fried portions of minced sardine muscle.

The aim of this work was to study the modifications occurring during frozen storage (-18 degrees C) of dressed and pre-fried portions of minced muscle of the sardine (Sardina pilchardus). Various samples were prepared in order to discover the effect on the samples of different preparatory frying times, the influence of vacuum-packing and the possible alterations in the state of preservation of the portions due to the presence of anti-oxidant agents. The results indicate that the presence of tocopherols did not have the expected effect on rancidity; it reduced the degree of rancidity reached during storage only slightly, while texture with respect to the control sample remained the same. Although the washed-muscle sample presented minimum rancidity values, the tasting panel awarded it the lowest score for acceptability. In contrast, the vacuum-packed sample presented less toughness and rancidity and was considered more acceptable, in the light of which this latter procedure would appear to be the best suited for frozen storage for pre-fried battered sardine portions.