Continuous High-pressure Cooling-Assisted Homogenization Process for Stabilization of Apple Juice

The effect of high-pressure homogenization (HPH) at 100–200 MPa (with up to 5 passes) on the quality and storage stability of apple juice was investigated. The microbiological quality, polyphenol oxidase (PPO), peroxidase (POD), polygalacturonase (PG) and pectinmethylesterase (PME) activity, particle size distribution (PSD), apparent viscosity, turbidity, concentration of vitamin C, individual polyphenols and their total content (TPC), antioxidant activity, and colour of fresh, HPH-treated apple juice were all evaluated. The highest reduction in microorganisms (1.4 log) and oxidoreductase activity (~20%) was observed at 200 MPa, while hydrolases did not change significantly. HPH led to significant disintegration of the tissue and a decrease in viscosity. Vitamin C decreased by 62%, while TPC increased by 20% after HPH. Significant correlations were observed between antioxidant activity, TPC, and individual polyphenols. Chlorogenic, ferulic, and gallic acid were most stable at 200 MPa. The optimal shelf-life of the juice was estimated as 7 days.

Functionalization of Enzymatically Treated Apple Pomace from Juice Production by Extrusion Processing

Food by-products can be used as natural and sustainable food ingredients. However, a modification is needed to improve the technofunctional properties according to the specific needs of designated applications. A lab-scale twin-screw extruder was used to process enzymatically treated apple pomace from commercial fruit juice production. To vary the range of the thermomechanical treatment, various screw speeds (200, 600, 1000 min−1), and screw configurations were applied to the raw material. Detailed chemical and functional analyses were performed to develop a comprehensive understanding of the impact of the extrusion processing on apple pomace composition and technofunctional properties as well as structures of individual polymers. Extrusion at moderate thermomechanical conditions increased the water absorption, swelling, and viscosity of the material. An increase in thermomechanical stress resulted in a higher water solubility index, but negatively affected the water absorption index, viscosity, and swelling. Scanning electron microscopy showed an extrusion-processing-related disruption of the cell wall. Dietary fiber analysis revealed an increase of soluble dietary fiber from 12.6 to 17.2 g/100 g dry matter at maximum thermo-mechanical treatment. Dietary fiber polysaccharide analysis demonstrated compositional changes, mainly in the insoluble dietary fiber fraction. In short, pectin polysaccharides seem to be susceptible to thermo-mechanical stress, especially arabinans as neutral side chains of rhamnogalacturonan I.

Browning of ‘Empire’ and ‘Fuji’ Apples as Affected by Antioxidant Activities

Internal ethylene concentration (IEC) and activities of peroxidase (POX), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) were analyzed to evaluate their effects on browning in late-harvested ‘Empire’ apples (Malus × domestica Borkh.), during air storage at 0.5 °C for five months, and for ‘Fuji’ apples treated with 1-methylcyclopropene (1-MCP), stored for seven months. IEC remained higher in the ‘Empire’ apples compared to values observed in the ‘Fuji’ apples for up to three months in storage, although 1-MCP treatment reduced the IEC in both fruit cultivars. Antioxidant enzymes, such as PPO, POX, and PAL, mostly increased in the flesh and core tissues in both 1-MCP-treated apple cultivars, but were slightly higher in the ‘Empire’ apples between one and three months of storage time. Browning developed in the ‘Empire’ apples after three months of storage, with high susceptibility to incidences of browning observed on the 1-MCP-treated fruit.

THERMAL ANALYSIS OF FOOD PRODUCTS USING DIFFERENTIAL SCANNING CALORIMETRY (DSC)

Intensity of changes during the freezing storage of frozen foods, depends on several factors. Changes of foods during freezing and thawing can be rapidly determined by scanning calorimetry (DSC). The aim of this study was to test the influence of scanning rate on the thermal properties of previously heat-treated food products (boiled apple), using the differential scanning calorimetry method. By increasing the scanning rate, significant changes (p0.05) Tcon from -14,20 °C (rate 5 °C/min) to -15.57 °C (rate 15 °C/min) and Tcend (from -17.53 °C to -22.90 °C) were determined, and ΔTc increased from 3.33 °C to 7.33 °C. At the same time, the width of the melting temperature interval (ΔTm) increased from 7.80 °C to 12.87 °C. The glass transition temperature (Tgmid) ranged from -7.15 °C (rate 5 °C/min) to -6.60 °C (rate 15 °C/min). Based on the obtained results, it was found that the scanning rate during the DSC determination statistically significantly (p0.05) influenced the measured values of the thermal properties of the tested heat-treated apple samples.

Effects of Instant Controlled Pressure Drop (DIC) Drying on the Texture and Tissue Morphology of Fruits and Vegetables

The effects of instant controlled pressure drop (DIC) drying, and blanching-assisted DIC (B + DIC) on texture, volume ratio (VR), colour, microstructures of different tissues, and cell-morphology of fruit and vegetable chips was examined. Results revealed that B + DIC had a significant effect on fruits and vegetable chips as compared with DIC treated. The DIC dried mango chips were observed to have low hardness (26.12 N) and maximum crispness (10.43) that were also observed in mango chips under B + DIC treated (14.66), exhibiting a puffy structure and crispy texture. Well expanded structure which reflected by VR was found in the mango (0.46 mL) and king oyster mushroom (KOM) (0.36 mL) chips under both treatments. The maximum total colour changes (∆E) were also obtained in the mango (30.40) and carrot (42.87) chips under B + DIC. The microstructures of the apple, carrot, KOM and potato chips products, which corresponded to its well expanded appearances, showed a honeycomb-like pores structure, observed for DIC treated apple, fresh potato, B + DIC dried KOM as well as in sweet potato. In addition, the B + DIC-treated carrot chips, pores size, increased the cell wall and expanded. Moreover, the mushroom chips mostly were shrunken after hot water blanching.