| Titre : | Investigation of the effect of temperature shifts on loss of quality and nutritional value of deshydrated food systems |
| Auteurs : | KAANANE Amar ; T.P Labuza |
| Type de document : | texte imprimé |
| Editeur : | University of Minnesota, 1984 |
| Format : | 204 p. |
| Langues: | Anglais |
| Index. décimale : | Q02 (Transformation et conservation des aliments) |
| Mots-clés: | ALIMENT ; TEMPERATURE ; DESHYDRATATION ; PERTE ; VALEUR NUTRITIVE |
| Résumé : |
Using the vapor pressure manometric method, the water activity of eight saturated salt solutions (aw ranging from 0.11 to 0.85) was determined at three different temperatures: 25, 30, and 45°C. The water activity of all salt solutions studied decreased as the temperature increased. A semilog plot of ln(1 − aw) for the different salt solutions versus the inverse of absolute temperature showed a linear relationship. A thermodynamic equation was derived to explain this decrease of aw in salt solutions when the temperature increases. The apparent heat of solution differed for each salt, explaining the differences in the effect of temperature. A higher Q10 gave a greater reduction.
Using a statistical t-test, it was found that the mean values of water activity of the different salt solutions determined by the VPM method differed from those suggested by the FDA and Greenspan at a 95 percent level of significance. Moisture sorption isotherms of fish flour were obtained at 25, 30, and 45°C using the gravimetric method. The sorption isotherms of the product at 65°C were determined using a flow method. The sorption isotherms obtained gave the characteristic S-shaped curve and showed that, at any moisture content, the water activity increases as the temperature increases, following a Clausius-Clapeyron relationship, opposite to the effect of temperature on salts. At temperatures greater than 25°C, a significant difference was found between the sorption isotherm obtained by plotting moisture content versus the aw of salt solutions found at 25°C and the one obtained by plotting moisture content versus the true aw of salt solution at the temperature of the study. It should be noted that many researchers do not use the correct aw at higher temperatures. Using the hygroscopic DT Kaymont instrument, fish flour equilibrated at different water activities and at 25°C was shifted up to 45°C in several steps at constant moisture content. The resultant shift was found to be predictable by the moisture sorption isotherm, indicating that the Clausius-Clapeyron equation applies to solid food moisture isotherms up to 65°C. These data also suggest a potential problem in stability for dry foods stored in sealed pouches and subjected to temperature shifts. Using an HP9816 computer, a statistical regression analysis was performed to evaluate the GAB equation and to compare this equation to the BET model. It was found that both equations give the same monolayer moisture content at all temperatures studied. Therefore, the GAB model represents an alternative to the BET model since it offers an objective method for drawing sorption isotherms up to 0.9 aw. The loss of lysine in fish flour stored in open and sealed pouches at 0.33, 0.44, and 0.65 water activities and at 25, 38, and 45°C was monitored during 22 weeks. The results of this study showed that the loss of lysine in fish flour appears to follow a first-order reaction throughout the storage period of 22 weeks. A statistical least squares analysis showed that the method of storage (open versus closed system) does not influence the rate of lysine loss in fish flour. The activation energy (Eₐ) and Q10 values for lysine losses in fish flour ranged respectively from 5.15 to 17.85 Kcal/mole and from 1.35 to 2.56 in the temperature range of 30 to 40°C. This study also showed that the specification for fish flour concerning loss of lysine during storage could not be met in reality. |
| En ligne : | http://10.2.0.27/PDF_CDA/uploads/PDF/KAANANE_Amar_1984_1007.pdf |
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| Code-barres | Cote | Support | Localisation | Section | Disponibilité |
|---|---|---|---|---|---|
| 100004795 | 1007 | Support papier | Salle des thèses/PFE (RDC) | Ingénieur Agronome | Consultation sur place Exclu du prêt |
