| Apple juice is very delicious, healthy and nutrient-dense food product. The production and processing of apple juice is ever increasing around the globe. China is the leading apple juice producer followed by the United States. Its processing relies mainly on conventional methods such as pasteurization and sterilization which have been associated with high thermal inputs. These methods could achieve the microbial safety and reduced enzymes activity of the product within desired shelf-stable level. Unfortunately, the intensities of treatment, time and process temperature are also proportional to the amount of nutrient loss, development of undesirable flavour and deterioration of functional properties. This is the driving force for the increased interest in alternative method of food processing and preservation. In this regard, ultrasound processing has received much attraction and attention in food technology during recent years for the production of fruit juices. Ultrasound is versatile and innovative technology due to its wide range of application. Effective mixing, increased mass transfer, reduced energy, low temperature and increased production rate are some of the merits of ultrasound processing. This technique is thought to be an effective and promising non-thermal method which may overcome the problems associated with heat treatments such as physical and chemical changes, nutritional loss and detrimental changes in sensory attributes. Its efficiency can be even further increased by coupling with either heat or pressure, or both heat and pressure.The main aim of the present study was, therefore, to evaluate the potential of sonication technology for apple juice processing along with its effect on various physicochemical parameters, enzymatic activities and microbiological characteristics of the finished product.Fresh apple juice treated with ultrasound (for 0,30,60 and 90 min, at 20 ℃, 25 kHz frequency) was evaluated for different physicochemical, Hunter color values, cloud value, antioxidant capacity, scavenging activity on 2,2-diphe nyl-1-picrylhydrazyl (DPPH) free radical, ascorbic acid, total phenolics, flavonoids, flavonols and microbial characteristics. No significant effect of sonication was observed on pH, total soluble solids (Brix) and titratable acidity of apple juice. Sonication significantly improved ascorbic acid, cloud value, phenolic compounds, antioxidant capacity, DPPH free radical scavenging activity and differences in Hunter color values. Moreover, significant reduction in microbial population was observed.The effects of sonication treatment on selected quality characteristics of apple juice such as polyphenolic compounds (chlorogenic acid, caffeic acid, catechin, epicatechin and phloridzin), sugars (fructose, glucose and sucrose), mineral elements (Na, K, Ca, P, Mg, Cu and Zn), total carotenoids, total anthocyanins, viscosity and electrical conductivity were examined. The fresh apple juice samples were sonicated for 0,30 and 60 min at 20 ℃ (frequency 25 kHz and amplitude 70%), respectively. As results, the contents of polyphenolic compounds and sugars significantly increased (P<0.05) but the increases were more pronounced in juice samples sonicated for 30 min whereas, total carotenoids, mineral elements (Na, K and Ca) and viscosity significantly increased (P< 0.05) in samples treated for 60 min sonication. Losses of some mineral elements (P, Mg and Cu) also occurred. Total anthocyanins, Zn and electrical conductivity did not undergo any change in the sonicated samples.Fresh apple juice was sonicated at 30,60 and 90% amplitude levels (temperature 20℃ and frequency 20 kHz) for 3 min keeping pulse durations of 5 Sec on/off. Samples were stored at 4℃ for 30 days. Effect of sonication and storage on total soluble solids (TSS), pH, titratable acidity, instrumental color (L*, a*, b*), non-enzymatic browning (NEB), cloud value, ascorbic acid and antioxidant capacity were evaluated. Additionally, the sensory characteristics were also investigated. As results, TSS, pH and acidity remained unchanged while, significant increase in color values, NEB, cloud value, ascorbic acid and antioxidant capacity was observed in all sonicated samples. Moreover, sensory quality was also improved as a result of sonication. Storage study showed significant increase in acidity, color values, NEB and decrease in pH, cloud value, ascorbic acid and antioxidant capacity without affecting the TSS of apple juice.Thermosonication technique using ultrasound in-bath (25 KHz,30 min,0.06 Wcm-3) and ultrasound with-probe sonicator (20 KHz,5 and 10 min,0.30 Wcm-3) at 20,40 and 60 ℃ was attempted for inactivation of enzymes (polyphenolase, peroxidase and pectinmethylesterase) and microflora (total plate count, yeast and mold) in apple juice. Additionally, ascorbic acid, total phenolics, flavonoids, flavonols, pH, titratable acidity, °Brix and color values influenced by thermosonication were investigated. The highest inactivation of enzymes was obtained in ultrasound with-probe at 60 ℃ for 10 min, and the microbial population was completely inactivated at 60 ℃. The retention of ascorbic acid, total phenolics, flavonoids and flavonols were significantly higher in ultrasound with-probe than ultrasound in-bath at 60 ℃. These results indicated the usefulness of thermosonication for apple juice processing at low temperature, for enhanced inactivation of enzymes and microorganisms.The combined effects of ultrasound (US) and high hydrostatic pressure (HHP) on enzymes (polyphenolase, peroxidase and pectinmethylesterase), microorganisms (total plate counts (TPC), yeasts and molds) and phenolic compounds (total phenols, flavonoids and flavonols) of apple juice were investigated. Moreover, changes in ascorbic acid, antioxidant capacity, scavenging activity on DPPH free radical, color values, pH, °Brix and titratable acidity were also evaluated. Fresh apple juice was treated with US (25 kHz and 70% amplitude) at 20 ℃ for 60min with subsequent HHP treatment at 250,350 and 450 MPa for 10min at room temperature. The results revealed that the combined US-HHP450 treatment caused highest inactivation of enzymes with complete inactivation of TPC, yeasts and molds. It also significantly improved the phenolic compounds, ascorbic acid, antioxidant capacity, DPPH free radical scavenging activity and color values.Overall, findings of the present study enumerated that sonication treatment could improve the quality of apple juice thereby enhancing its nutritional status with special reference to increased phytonutrients and reduced enzymatic and microbial activity. It may successfully be employed for commercial apple juice processing with improved quality and safety from consumer’s health point of view. Further, the combination of US and HHP can act as a potential hurdle to produce safe and good quality apple juice without compromising its physicochemical characteristics. |
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