The aim of this work was to demonstrate how ultrasound mechanisms (direct and indirect effects) improve the mass transfer phenomena in food processing, and which part of the process they are more effective in. Two model cases were evaluated: the hydration of sorghum grain (with two water activities) and the influx of a pigment into melon cylinders. Different treatments enabled us to evaluate and discriminate both direct (inertial flow and "sponge effect") and indirect effects (micro channel formation), alternating pre-treatments and treatments using an ultrasonic bath (20 kHz of frequency and 28 W/L of volumetric power) and a traditional water-bath. It was demonstrated that both the effects of ultrasound technology are more effective in food with higher water activity, the micro channels only forming in moist food. Moreover, micro channel formation could also be observed using agar gel cylinders, verifying the random formation of these due to cavitation. The direct effects were shown to be important in mass transfer enhancement not only in moist food, but also in dry food, this being improved by the micro channels formed and the porosity of the food. In conclusion, the improvement in mass transfer due to direct and indirect effects was firstly discriminated and described. It was proven that both phenomena are important for mass transfer in moist foods, while only the direct effects are important for dry foods. Based on these results, better processing using ultrasound technology can be obtained.

The influence of ultraviolet irradiation (UV) on some quality attributes (colour, pH, soluble solids content, formol index, total phenolics, sugars and vitamin C) and enzymatic activities (polyphenol oxidase, peroxidase and pectinolytic enzymes) of fresh apple juice was investigated. Apple juices made from four different varieties (Golden, Starking, Fuji and King David) were irradiated during 120 min with a high-pressure mercury lamp of 400 W that emits in a range between 250 and 740 nm with a resulting incident energy of 3.88·10 −7 E·min −1 . The treatment was effective in the inactivation of the assayed enzymes. Polyphenol oxidase was inactivated in 100 min, while peroxidase was completely destroyed in only 15 min in all the four varieties. No variations were observed in pH, soluble solids content, formol index, total phenolics and sugars. The colour of the juice made from King David was unvariable during all the experiment. In the ones made from Golden, Starking and Fuji, UV radiation impaired some of the pigments present in the juice, either initially present or the ones formed later. This fact can be especially observed in the increase of the CIELab parameter L*, which increased from 23.2 to 24.6 in Fuji juice. The content of vitamin C in juices from Golden, Starking and Fuji slightly changed during the experiment, decreasing a 4.0% in Fuji juice, 5.7% in Golden one and 5.6% in Starking one. Meanwhile, in the juice from King David the loss was 70.0%. This significant difference can be attributed to the lack of pigmentation of this juice. Keywords Ultraviolet irradiation Apple juice Poyphenol oxidase Peroxidase Colour 1 Introduction Food safety is one of the most important issues facing food industries and food service companies. Currently, the growing demand for a greater variety of prepared food and dishes on a menu makes the risk of contamination increases, especially due to the characteristics of this kind of food that gives a great importance to the quickness of meals. The application of HACCP (Hazard Analysis and Critical Control Points) has increased security guarantees in production systems, thermal treatments and cold chains, helping to reduce the opportunities for pathogens to gain access to food and/or grow to levels that will pose a risk of infection or toxin production. However, the incidence of foodborne diseases continues to rise in most industrialized countries ( Bintsis, Litopoulou-Tzanetaki, & Robinson, 2000 ). Moreover, in recent times the demand by consumers for minimally processed foods with characteristics as similar as possible to fresh products, has increased rapidly. Currently, heat treatment process is the most commonly used hurdle for inactivating microorganisms and enzymes, extending products shelf-life. However, this process may have adverse effects on sensory and nutritional quality of food ( Braddock, 1999 ). In this context, non-thermal technologies have received increasing attention in recent years, especially in the preservation of beverages, due to its potential for inactivating spoilage and pathogenic microorganisms. In addition, some of these techniques can help to minimize the loss of quality in terms of flavor, colour and nutritional value ( Noci et al., 2008 ). UV radiation has been used for decades to disinfect water, being an effective method for microbial decontamination of surfaces and packaging in the food industry ( Bintsis et al., 2000 ). The main limitations of UV application are related to the low penetration and the effect reduction in the presence of suspended solids. In distilled water, UV radiation at 254 nm suffers a loss of 30% of its intensity 40 cm below the surface, while the sea water will cause the same reduction in just 10 cm. A 10% sucrose solution or water with high iron levels cause the same loss in 5 cm ( Guerrero-Beltrán & Barbosa-Cánovas, 2004; Snowball & Hornsey, 1988 ). Regarding the preservation of the organoleptic and nutritional quality some research has shown promising results in the exposure of apple juice to UV irradiation ( Harrington & Hills, 1968 ). Currently, in the manufacture of fruit juices, the FDA requires to apply a preservation method capable of reducing pathogens at least 5 logarithmic cycles ( FDA, 2000 ). They also approved ultraviolet irradiation as a suitable method for the preservation of fruit juices, just if the turbulent flow conditions can be ensured throughout the treatment process. However, this requirement is not necessary when UV radiation is not the only hurdle. Most of the studies about UV irradiation of fruit juices have been carried out in order to assess its effect in microbial inactivation. Nevertheless, there are few references about UV influence on some enzyme activities that are important in this kind of fruit derivatives, especially tyrosinase, which is responsible of enzymatic browning in vegetable tissues containing phenolic or polyphenolic compounds ( Falguera, Pagán, & Ibarz, 2010 ). In this work, the effect of UV irradiation on apple juices from 4 varieties has been assayed, measuring some physicochemical properties and the activities of some enzymes (including tyrosinase, peroxidase and pectinolytic enzymes). 2 Material and methods 2.1 Juice preparation Apples from the four different varieties (Golden, Starking, Fuji and King David) were washed, peeled and kept in water while waiting to be cut in four and squeezed with a household juicer. The resulting juice was centrifuged in an Avanti J-26XP Centrifuge (Beckman Coulter, USA) for 25 min at 13,000 rpm. This process was done at 4 °C to make separation of supernatant easier and to reduce enzymatic activities After centrifugation was complete, the supernatant was recovered and the pellet was discarded. Fractions of 800 mL of juice were stored in the freezer. 2.2 UV processing UV irradiation was carried out in a dark chamber containing the juice and the lamp. Apple...