J.M. Quevedo

Effects of High-Pressure Treatment on the Sensory Quality of White Grape Juice

The effects of high-pressure treatment on the colour (objective measurement) and sensory characteristics of white grape juice were studied during storage at 4 °C for 60 days. Grape juice was subjected to three different treatments: 400 or 500 MPa at 2 u °C, and 400 MPa at 40 °C during 10 min. Untreated juice was used as control. Colour parameters (CIE L * a * b *), hue angle (tan m 1 b */ a *), chroma {( a * 2 + b * 2 ) 1/2 }, luminosity Q *{(10 2 log( L *) + 100} and saturation S *( C */ L *) were measured. Juices were evaluated for sweetness, acidity, off-flavour and aroma. High-pressure treatments did not affect the colour parameters of juice, and similar sensory characteristics were observed in both control and treated samples on the first day. The colour and sensory characteristics of pressure-treated samples remained more stable than those of the control juice during 60 days of storage. The control juice was slightly fermented developing some changes in flavour and colour.

Effects of ultra-high-pressure homogenization treatment on the lipolysis and lipid oxidation of milk during refrigerated storage.

Free fatty acid (FFA) release and quantification and lipid oxidation extent of ultra-high-pressure homogenized (UHPH) milk samples were evaluated to assess the effect of UHPH on the susceptibility of milk lipids to lipolysis and oxidation. Milk was UHPH-treated at 200 and 300 MPa with inlet temperatures of 30 and 40 degrees C. UHPH-treated samples were compared to high-pasteurized milk (PA; 90 degrees C, 15 s). Results showed that all FFA increased significantly during storage only in 200 MPa samples. Lipid oxidation was measured as an accumulation of lipid hydroperoxides as the primary oxidation product and malondialdehyde and hexanal as the secondary oxidation products. Samples treated at 300 MPa presented higher malondialdehyde and hexanal content compared to 200 MPa treated-samples and to PA milk.

Ultra-high pressure homogenisation of milk: technological aspects of cheese-making and microbial shelf life of a starter-free fresh cheese.

Fresh cheeses from pasteurised (80 °C for 15 s), homogenised-pasteurised (15 + 3 MPa at 60 °C; 80 °C for 15 s) or ultra-high pressure homogenised milks (300 MPa and inlet temperature of 30 °C) were produced in order to evaluate different technological aspects during cheese-making and to study their microbial shelf life. Although the coagulation properties of milk were enhanced by ultra-high pressure homogenisation (UHPH), the cheese-making properties were somewhat altered; both conventional homogenisation and UHPH of milk provoked some difficulties at cutting the curd due to crumbling and improper curd matting due to poor cohesion of the grains. Cheese-milk obtained by UHPH showed a higher microbiological quality than milk obtained by conventional treatments. Starter-free fresh cheeses made from UHPH-treated milk showed less syneresis during storage and longer microbiological shelf-life than those from conventionally treated milk samples.

Microbiological and Sensory Effects of Musts Treated by High-pressure Homogenization

The winemaking sector needs to ensure the microbiological quality of its products to guarantee acceptance and wide commercialization. There are treatments such as high pressure homogenization (HPH) that, apparently, do not affect the final nutritional and sensory food properties. This study is presented to evaluate possibilities of utilizing HPH treatments to reduce the indigenous flora accompanying wine musts, as well as their effects on the fermentative process, oenological parameters, color, aroma, and taste properties. Two different must varieties were used: a white must (Parellada variety) and a red one (Trepat variety). Results showed that the use of HPH at 200 MPa is capable of reducing the microbial load of musts. Residual populations of total bacteria were detected, but neither fungi, nor yeasts, nor lactic acid bacteria were detected after the treatment in either musts. Furthermore, as a result of the decrease of the wild microbiota of the musts, the implantation of the selected yeast for alcoholic fermentation was improved. Sensory assessments of the must and wines showed that there were no significant changes caused by the treatment.