The effect of carboxymethylcellulose (CMC) on the aggregation of formulation based on calcium caseinate, commercial whey protein (WPC), and a 1:1 mixture of soy protein isolate (SPI) and whey protein isolate (WPI) was investigated. Protein aggregation could be observed upon addition of CMC, as demonstrated by size-exclusion chromatography. This aggregation behaviour was enhanced by means of physical treatments, such as heating at 90°C for 30 min or gamma-irradiation at 32 kGy. A synergy resulted from the combination of CMC to gamma-irradiation in Caseinate/CMC and SPI/WPI/CMC formulations. Furthermore, CMC prevented precipitation in irradiated protein solutions for a period of more than 3 months at 4°C.

In order to enhance the shelf-life of a late variety of Moroccan Citrus clementina (Nour), ionizing treatments were applied at 0.3kGy, as well as washing (cold water) and waxing treatments. It has been found that, despite the irradiation treatment, the washing and waxing treatment do not improve the quality of C. clementina, but rather result in peel injury. Finally, sensory evaluation confirmed that irradiation had no detrimental effect on the quality of clementines.

ABSTRACT: Gamma‐irradiation and various edible coatings were tested on fresh strawberries (Fragaria spp.) for keeping fruit quality and extending shelf life. Four coatings based on milk protein were evaluated. In 1 experiment, coating formulation based on caseinate and/or strawberries were irradiated using a 60Co source. Both gamma‐irradiation treatment and edible coating process significantly delayed (p ≤ 0.05) molds growth. Edible coating based on irradiated caseinate was more effective than that of unirradiated caseinate. In a 2nd experiment, 3 irradiated coatings based on calcium caseinate and whey proteins were evaluated. The coating formulation based on 1:1 caseinate‐whey was found to be more effective than those based on calcium caseinate. Addition of calcium chloride or a mixture of pectin and agar increased the effectiveness of the coating by delaying molds' apparition.

The contribution of thermal and radiative treatments as well as the presence of some excipients, namely glycerol, carboxymethylcellulose (CMC), pectin, and agar, on the formation of protein-protein interactions as well as the formation and loss of protein-water interactions was investigated by means of differential scanning calorimetry in an isothermal mode. Protein-water interactions were assessed through measurement of the heat of the wetting parameter. Isothermal calorimetry measurements pointed out that gamma-irradiation does not favor protein-water interactions, as reflected by its endothermic contribution (P < or = 0.05) to the heat of wetting values. Although significant (P < or = 0.05), the effect of the thermal treatment on endothermic responses using isothermal calorimetry was found to be somewhat lower. Among excipients added to biofilm formulations, glycerol generated the most important losses of protein-water interactions, as inferred by its significant (P < or = 0.05) endothermic impact on the heat of wetting values.

To enhance the shelf life of a late variety of Moroccan Citrus clementina (Nour), ionizing treatments were applied at 0.3 kGy, as well as washing (cold water) and waxing treatments. It has been found that, despite the irradiation treatment, the washing and waxing treatment do not improve the quality of C. clementina, but rather result in yellower peels, peel injury, and reductions of vitamin C content, acidity, and soluble solids. However, gamma-irradiation alone enhanced significantly (p <or= 0.05) the level of vitamin C and the total phenolic content and maintained the color of the C. clementina during the entire storage period (49 days at 3 +/- 1 degrees C and 84% relative humidity). Finally, sensory evaluation further confirmed the beneficial effect of gamma-irradiation. Irradiated clementines were found to be sweeter. Also, the sensorial score of irradiated (I) and washed, waxed, and un-irradiated (LC) fruits was maintained over 7 days during 21 days as compared to 14 days for unwashed, unwaxed, and un-irradiated (C) and for washed, waxed, and irradiated (LCI) fruits.

In order to enhance the shelf-life of edible mature mushrooms Agaricus bisporus, 2kGy ionising treatments were applied at two different dose rates: 4.5kGy/h (I−) and 32kGy/h (I+). Both I+ and I− showed 2 and 4 days shelf-life enhancement compared to the control (C). Before day 9, no significant difference (p>0.05) in L* value was detected in irradiated mushrooms. However, after day 9, the highest observed L* value (whiteness) was obtained for the mushrooms irradiated in I−. Analyses of phenolic compounds revealed that mushrooms in I− contained more phenols than I+ and C, the latter containing the lower level of phenols. The polyphenol oxidase (PPO) activities of irradiated mushrooms, analysed via catechol oxidase and dopa oxidase substrates, resulted in being significantly lowered (p⩽0.05) compared to C, with a further decrease in I+. Analyses of the enzymes indicated that PPO activity was lower in I+, contrasting with its lower phenol concentration. Ionising treatments also increased significantly (p⩽0.05) the phenylalanine ammonia-lyase (PAL) activity. The observation of mushrooms cellular membranes, by electronic microscopy, revealed a better preserved integrity in I− than in I+. It is thus assumed that the browning effect observed in I+ was caused by both the decompartimentation of vacuolar phenol and by the entry of molecular oxygen into the cell cytoplasm. The synergetic effect of the residual active PPO and the molecular oxygen, in contact with the phenols, allowed an increased oxidation rate and, therefore, a more pronounced browning in I+ than in I−.

Free-standing sterilized edible films based on milk proteins, namely calcium caseinate and whey protein isolate, and polysaccharides, namely pectin and agar, were developed. Cross-linking of the proteins was achieved by the combination of thermal and radiative treatments. Autoclaving pectin and agar prior to their addition to the protein solutions generated films with an improved (P < or = 0.05) puncture strength. The presence of proteins and pectin-agar in the film formulation enhanced (P < or = 0.05) the moisture barrier of the films by 18%. A strain of Streptococcus thermophilus was used to assess the biodegradability behavior of the cross-linked films. Microbiological counts and soluble nitrogen analysis confirmed the biodegradability property of the milk protein films containing autoclaved pectin and agar.

Sterilized biofilms based on soy protein isolate (SPI, S system) and a 1:1 mixture of SPI and whey protein isolate (WPI, SW system) were achieved through the formation of cross-links by means of gamma-irradiation combined with thermal treatments. The effect of the incorporation of carboxymethylcellulose (CMC) and poly(vinyl alcohol) was also examined. gamma-Irradiation combined with thermal treatment improved significantly the mechanical properties, namely, puncture strength and puncture deformation, for all types of films. Irradiated formulations that contain CMC behave more similarly as elastomers. CMC showed also significant improvements of the barrier properties, namely, water vapor permeability, for irradiated films of the S system and for non-irradiated films of the SW system.

Ionizing treatments were applied at 0.5 kGy, 1.5 kGy, and 2.5 kGy to edible mature mushrooms (Agaricus bisporus, albidus) in order to assess the effect of the gamma-irradiation on some biochemical parameters. Irradiation at doses of 1.5 kGy and 2.5 kGy reduced significantly (p < or = 0.05) the rate of respiration of the mushrooms, compared to that of samples irradiated at 0.5 kGy and nonirradiated control samples (C). Ionizing treatments increased significantly (p < or = 0.05) the phenylalanine ammonia-lyase (PAL) activity and total phenols concentration between days 1 and 4. From days 3-4, to the end of the storage period (day 12), both PAL activity and total phenols in the irradiated samples (I) collapsed to lower values. In contrast, the activity of polyphenol oxidase (PPO) increased until days 7, 9, and 12 for samples treated at 0.5, 1, and 2 kGy, respectively. Color measurements showed a loss of whiteness (L value) during storage. After day 4, however, the effectiveness of gamma-irradiation became apparent, and highest L values were obtained for I only.

gamma-Irradiation was used to produce free-standing sterilized edible films based on caseinate. The effects of calcium ions (Ca(2+)) and two plasticizers, namely propylene glycol (PG) and triethylene glycol (TEG), were investigated, as was the effect of the irradiation on both the gel formation and mechanical properties of the resulting films. gamma-Irradiation provoked formation of bityrosine, i.e., cross-links, accounting for the increase of the puncture strength of films. The presence of PG or TEG enhanced the formation of cross-links, leading to an improved mechanical strength of films. TEG was found to interact more favorably with the caseinate than PG, being responsible for the improved film extensibility. Addition of Ca(2+) caused the formation of gels. The breaking strength of gels was directly related to the concentration of Ca(2+), while the puncture strength of films was found to be almost independent of the calcium concentration. Moreover, a high irradiation dose seemed to affect the protein structure, accounting for the decrease of the breaking strength of gels and for the depreciation of the mechanical behavior of films.