The objective of this work was to simulate heat transfer during blanching (90 °C) and hydrocooling (5 °C) of broccoli florets (Brassica oleracea L. Italica) and to evaluate the impact of these processes on the physicochemical and nutrimental quality properties. Thermophysical properties (thermal conductivity [line heat source], specific heat capacity [differential scanning calorimetry], and bulk density [volume displacement]) of stem and inflorescence were measured as a function of temperature (5, 10, 20, 40, 60, and 80 °C). The activation energy and the frequency factor (Arrhenius model) of these thermophysical properties were calculated. A 3-dimensional finite element model was developed to predict the temperature history at different points inside the product. Comparison of the theoretical and experimental temperature histories was carried out. Quality parameters (firmness, total color difference, and vitamin C content) and peroxidase activity were measured. The satisfactory validation of the finite element model allows the prediction of temperature histories and profiles under different process conditions, which could lead to an eventual optimization aimed to minimize the nutritional and sensorial losses in broccoli florets.

Constant retort temperature (CRT) processes for thermally treated foods are usually time-consuming and have drastic impact on food quality. Variable retort temperature (VRT) processes may decrease the processing time and may retain better the food nutritional quality. Five isolethal profiles (one CRT and four VRT) for preparing papaya puree (pH 3.8) were designed using pectin methyl esterase as the target enzyme for thermal processing, and their effect on the puree quality was evaluated. The objective was to compare these profiles based on processing time, vitamin C retention, consistency index and color. The VRT isolethal profiles reduced the processing time up to 33.3% compared with CRT, whereas vitamin C, consistency index and chroma were retained up to 65, 71 and 89%, respectively, compared with fresh puree. The best resulting treatment was a VRT upstairs profile (75C/19 min, 80C/8.5 min, 90C/10.7 min and 6C/20.8 min). The results show that the use of VRT profiles allows retaining the nutritional quality of canned papaya puree. PRACTICAL APPLICATIONSThis research explored the use of variable retort temperature to increase product quality and improve processing time in canning of papaya puree. In an upstairs profile, 65% of vitamin C was retained compared with fresh product. The results would be useful for canning of conduction-heated foods.

Pineapple slices were treated with three antioxidants and stored under passive modified atmosphere packaging (MAP) to evaluate the effect of these treatments on tissue browning (percentage of dark area) and the accumulation of ascorbic acid and total phenolics. Pineapple slices were immersed in ascorbic acid (AA), isoascorbic acid (OAA), and N-acetylcysteine (NAC) solutions for 2 min, and then were packed and stored at 5 °C under air (AOR) or MAP for 15 days. Water was used as control. The application of OAA and NAC under passive MAP reduced better the tissue browning index and maintained a good quality of the slices. The use of AA and OAA increased the contents of ascorbic acid and total phenolics. The application of OAA followed by storage under MAP conditions was effective in reducing tissue browning, which was associated with a higher retention of ascorbic acid and total phenolics contents of the pineapple slices.

The objective of this work was to ®nd the best combinations of ascorbic acid concentration/ soaking time (Pretreatment 1), 4-hexylresorcinol concentration/soaking time (Pretreatment 2) and ascorbic acid concentration±4-hexylresorcinol concentration/soaking time (Pretreatment 3) to prevent the development of enzymatic browning in raw potato cubes (10 mm  10 mm  10 mm). Potato variety Alpha was used as study model because of its low susceptibility to enzymatic browning. Response surface methodology was applied in all pretreatments on two response variables (Hunter L value and total colour difference) to ®nd the best conditions for carrying out the pretreatments. The various pretreatments had variation levels for ascorbic acid (AA) concentration (1 and 3) and 4-hexylresorcinol (4HR) concentration (2 and 3) of 1±4 and 0.04±0.20 g l À1 respectively; in all pretreatments the variation level for soaking time was 3±6 h. A central composite experimental design with two factors at ®ve levels was used. Predictive models for Hunter L value and total colour difference were developed as a function of process or independent variables. The optimisation technique was applied to obtain maximum Hunter L values and minimum values of total colour difference.