M. Dalla Rosa

Effect of ultrasound treatment on the water state in kiwifruit during osmotic dehydration

The present work investigates how ultrasound pretreatment modulates the effects of osmotic dehydration (OD) on the water state and microstructure of kiwifruit. Kiwifruit slices (10mm thick) were subjected to ultrasonic waves in a water bath at a frequency of 35 kHz for 10, 20 and 30 min. OD process was then carried out by immersing the samples in 61.5% sucrose solution equilibrated at 25°C for a contact period of 0, 10, 20, 30, 60 and 120 min. The partition of water into the cellular tissue structures (vacuole, cytoplasm, extracellular spaces and cell wall) was investigated by Time Domain Nuclear Magnetic Resonance (TD-NMR). In parallel, the microstructure of kiwifruits slices was examined using a Scanning Electron Microscope. The results showed that US pretreatment performed for more than 10 min had a positive effect on the mass exchange caused by osmotic dehydration. A creation of microchannels and an increase of the average cross-section area of cells were observed when the samples were pretreated with US before OD. TD-NMR showed a slight redistribution of water through the substructures of the cells, as a function of the length of the US pretreatment applied.

Physical, chemical, textural and sensorial changes of portioned Parmigiano Reggiano cheese packed under different conditions

Changes in physical (colour), chemical (moisture content and proteolysis index), texture and sensory characteristics of differently packed portioned Parmigiano Reggiano cheese were monitored during three months of storage at 4°C. Packaging conditions were under vacuum (UV) and in modified atmosphere (MA) with 50:50 (MA1) and 30:70 (MA2) CO 2/N2 ratios. The results showed, in general, substantial changes in the differently packed products. All samples underwent proteolysis phenomena together with changes in the textural and sensory characteristics. The UV packed sample showed the occurrence of an oil dropping up phenomenon which caused significant changes in product characteristics such as an increase of cohesion, sourness and yellowness. The MA packed samples showed different textural behaviour (MA2 sample evolved towards a more cohesive and friable structure than MA1) and a similar evolution of the flavour profile that, after 90 days of storage, determined a softer taste than the unpacked cheese. Parmigiano Reggiano cheese hardness showed discordant results according to the testing method (compression, shear or shear—compression), whether it involved the fracture of cheese structure or not.

Microbial aspects on short-time osmotic treatment of kiwifruit

Abstract In order to study the influence of solution concentration on the microbiological quality of fruit after osmotic dehydration, Kiwifruit slices have been immersed for three hours into osmotic solutions, inoculated with Metschnikowia pulcherrima , at different concentrations (from 40° to 65° Brix) to obtain high moisture fruit products. Microbial adhesion kinetic to the fruit surface was studied: the number of adhering cells was affected by the sucrose concentration of the osmotic solution and the microbial adhesion was strongly reduced at high sugar concentration (65° Brix). Samples were packed in LDPE bags under air atmosphere and preserved at refrigeration temperature. Microbial load of inoculated and osmotically treated kiwifruit slices was determined during eighteen days of storage time. A mathematical model based on the Zwietering modified Gompertz equation, was used to obtain growth parameters of the yeast and to outline the microbial evolution of osmodehydrated Kiwifruit slices during storage. Storage data showed that, the microbial load was the lower, when higher the solution concentration used for the osmotic dehydration.

Freeze-dried strawberries rehydrated in sugar solutions: mass transfers and characteristics of final products

Sugar solutions with different sugar composition and concentration were used to reconstitute freeze-dried strawberries. The mass transfer between fruit pieces and solution during the rehydration process and the physicochemical characteristics of the reconstituted products were evaluated. The results indicated that by varying the concentration of the sugar solution and reconstitution time it was possible to obtain from the same freeze-dried product, rehydrated fruit pieces with different and peculiar characteristics such as water activity, freezing point, amount of freezable water and firmness. In addition, these characteristics were linearly correlated with soluble solids content in the rehydrated products. Using the above method, the reconstituted freeze-dried strawberries are able to be used as an ingredient in formulated foods at different levels of water activity and also in frozen dessert or ice cream.

Modified atmosphere packaging of hen table eggs: Effects on functional properties of albumen

The aim of this study was to compare technological properties (gel hardness, foam drainage, and meringue crispness) of albumen of nonpacked table eggs (control) with those of eggs packed in high-barrier plastic pouches with 3 modified atmosphere packaging (MAP) conditions (air, 100% N(2), and 100% CO(2)) during 28 d of storage at 25°C. The values of gel hardness for the control sample showed an increasing trend, demonstrating the highest values throughout the experiment duration compared with the other samples. This behavior was probably attributable to the pH increase detected only for this sample during storage (from 8.82 ± 0.06 for fresh egg to 9.96 ± 0.06 at the end of the experiment). Air and N(2) samples showed constant and similar hardness values during storage. The hardness of coagulated albumen showed a strict correlation with raw albumen pH (r(2) = 0.929; P < 0.001). Other than reducing albumen pH during storage, MAP with CO(2) caused the formation of a soft and puffy coagulum with very low hardness, reaching the lowest value of 1.26 ± 0.38 N after 4 d of storage, that slowly increased to 2.11 ± 0.49 N at the end of the experiment. Foam stability decreased during storage for all samples, but CO(2) eggs showed a significantly (P < 0.05) higher foam stability than fresh eggs until 15 d, reaching values similar to those of the other samples only at the end of the storage time. Packing eggs in CO(2) promoted an improvement of meringue crispness. The application of this atmosphere could ameliorate the quality characteristics of albumen-based food products. Commercially, CO(2) MAP could provide an albumen-based ingredient tailored to maximize the characteristics needed in the final product (e.g., fresh shell eggs special for meringue preparation) that could give an added value to the product.

Effects of chitosan based coatings enriched with procyanidin by-product on quality of fresh blueberries during storage

The aim of this work was to evaluate the efficacy of an innovative edible coating, based on chitosan from mushrooms enriched with procyanidins extracted from grape seeds, on fresh blueberry quality maintenance, (weight loss, pH, dry matter, colour, firmness and antioxidant activity) and microbial growth, during 14 days of storage at 4 °C. For weight loss, pH and dry matter no relevant differences were detected among the control and the differently coated samples at each considered storage time. Chitosan and chitosan + procyanidins coatings promoted a slight decrease of luminosity and an increase of blue hue colour of blueberry samples during the whole storage period. The use of coating promoted an increase in the antiradical activity that was the highest in blueberries coated with chitosan + procyanidins. Microbiological analysis results indicated that the chitosan-based coated samples had a significantly higher yeast and mould growth inhibition compared to the uncoated sample.

Effect of Pulsed Electric Fields on Water Distribution in Apple Tissue as Monitored by NMR Relaxometry

Pulsed electric fields (PEF) technology is a promising innovative non-thermal process to improve mass transfer in food sector. PEF treatments induce a partial cell membranes electroporation which extent depends on electric field strength, number, duration and shape of the pulses and application time. The present work aimed at highlighting the effect of the application of PEF on mass transfer phenomena in apple parenchyma tissue, by evaluating the water distribution across cell compartments by means of NMR relaxometry. Pulsed electric fields treatments were carried out using near-rectangular shaped pulses with fixed 100 μs pulse width and 10 ms repetition time at three different specific voltage (100, 250 and 400 V cm− 1) and two different pulse number series (n=20 and n=60).