Abstract
Topical consumer interest in natural, healthier, safer and nutritional juice, has inspired the search for innovative technologies that can minimize product degradation. In this regard, thermosonication has been proposed as a potential processing technology that can preserve and produce "fresh" products. Watermelon (Citrullus lanatus) juice is a nutrient-rich fruit juice that is desired by consumers due to its appealing color, pleasant odor, sweet taste and low-calorie content. This fruit juice is, however, highly perishable and prone to microorganisms, because of its neutral pH value and high amount of water activity. In addition, it is thermo-sensitive and therefore degrades quickly under thermal processing. This study aimed to identify the optimal thermosonication processing conditions for retaining the critical quality parameters (lycopene, β-carotene, ascorbic acid and total polyphenolic content) of watermelon juice. Response surface methodology, employing a central composite design, was used to determine the effects of temperature (18-52 °C), processing time (2-13 min) and amplitude level (24-73 μm) at a constant frequency of 25 kHz. The highest quality parameters were obtained at 25 °C, 2 min, and 24 µm at a constant frequency of 25 kHz, which resulted in lycopene of 8.10 mg/100 g, β-carotene of 0.19 mg/100 g, ascorbic acid of 3.11 mg/100 g and total polyphenolic content of 23.96 mg/GAE/g with a desirability of 0.81. The proposed model was adequate (p < 0.0001), with a satisfactory determination coefficient (R2) of less than 0.8 for all phytochemicals. Thermosonicated watermelon juice samples showed minimal changes in their phytochemical properties, when compared to fresh juices; the lycopene content showed a significant increase after thermosonication, and a significant retention of β-carotene, ascorbic acid and total polyphenolic acid was observed. According to the findings, thermosonication could be a viable method for preserving watermelon juice, with minimal quality loss and improved functional attributes.