The juice industry is experiencing a positive and dynamic growth, largely driven by consumer preferences for healthier products, evolving lifestyles, and increased disposable income. Globally, there is a diminishing demand for soft drinks such as aerated water and flavoured soda due to their high sugar content, artificial additives (colours and sweeteners), as well as potentially harmful elements like phosphoric acid and caffeine. These factors are recognized for their adverse effects on human health. Fruit juices are categorized as "new age beverages" (Priyadarshini and Priyadarshini 2018) and increasingly opted by consumers. Juice manufacturers are adapting to this shift by incorporating healthier ingredients, aligning with the growing consumer preference for better options. Worldwide, manufacturers are introducing innovative and diverse products, aiming to enhance sales through creative flavour combinations, adjustments in calorie, sweetness levels and practical features that align with prevailing lifestyle trends.
The pure fruit juices pose challenges in terms of storage, packaging, and transportation due to their large volume, as well as susceptibility to both nutritional and sensory deterioration. Concentration of aqueous foods is a major unit operation in the food industry (Deshpande et al. 1984). The process of concentrating liquid foods involves reducing the volume of the liquid while, maintaining or intensifying its flavour and nutritional content. In contrast, fruit juice concentrates offer an extended shelf life and are more convenient, cost effective, energy efficient to pack, store, and transport over long distances. The concentration process reduces water activity (Aw), thereby hindering the growth of microorganisms and enhancing the overall shelf life of juice products. (Adnan et al. 2018). If the concentration process done correctly, the juice concentrate can be diluted with water to resemble the original juice qualities (Vatai, 2013).
Different methods are employed in concentration of fruit juices involves evaporation (traditional and thin film evaporation) reverse osmosis (Rastogi 2018), freeze concentration (Ding et al. 2019), spray drying (Goula and Adamopoulos 2010), membrane filtration, pervaporation (Aroujalian and Raisi 2007), centrifugation (Petzold et al. 2015) and vacuum concentration (Bozkir and Baysal 2017).
The food industry has long utilized the vacuum technique, which contributes positively to the quality of the final product by preventing oxidation reactions, overheating, and heat damage (Berk 2008). The working principle of the vacuum concentrator is explained by the following theory that the state of a substance is influenced by two main factors, heat and pressure. The temperature at which boiling or vaporization happens depends on the pressure applied. In vacuum concentrators, a vacuum is used to lower the boiling point of a solvent, causing liquid vaporization at lower temperatures. However, the pressure is insufficient for liquid formation, causing the solvent to change directly from solid to gas (sublimation). The resulting vapour is removed by a cold trap or condenser, allowing the recovery of the solvent (Petzold et al. 2013). Vacuum concentrators evaporate volatile samples by using a combination of centrifugal force, heat, and vacuum (Romniou et al. 2022). The technique is applied to drying, purification, evaporation, and particularly quick concentration.
Dragon fruit, also known as pitaya, belongs to the Cactaceae family and originates from tropical areas in Mexico, Central America, and South America (Mizrahi et al. 1997). Additionally, it is extensively cultivated in various Asian nations, including Malaysia, Vietnam, Thailand, the Philippines, and Taiwan. Various cultivars of dragon fruit have been developed for commercial fruit production, such as Hylocereus undatus (characterized by a red pericarp and white pulp), H. megalanthus (featuring a yellow pericarp and white pulp), H. polyrhizus (with a red pericarp and red-purple pulp), and H. costaricensis (displaying a red pericarp and red pulp) (Arriffin et al. 2009).
Dragon fruit, renowned for its stunning appearance, offers a myriad of health benefits. Rich in vitamin C (5.64 mg 100g− 1), this exotic fruit supports immune function, helping the body ward off illnesses and infections. The presence of B vitamins (niacin and pyridoxine) and essential minerals like phosphorus, potassium, calcium, magnesium, manganese, copper, zinc and iron, contributes to overall well-being, promoting healthy metabolism and cellular function (Arivalagan et al. 2021). Dragon fruit's high fiber content aids in digestion, supporting a healthy gut and potentially assisting in weight management (Pansai et al. 2020). Moreover, the fruit's antioxidants combat oxidative stress, reducing inflammation and supporting cardiovascular health (Joshi and Prabhakar 2020). With its low calorie and cholesterol-free nature (Wichienchot et al. 2010), dragon fruit emerges as a nutritious choice for those seeking to enhance their diet, providing a delicious way to incorporate essential nutrients into a balanced and health-conscious lifestyle. This study aims to investigate the impact of process variables, specifically temperature and time, on the vacuum concentration of dragon fruit juice. By systematically analyzing these factors, we aim to optimize the concentration process for enhanced efficiency and quality in dragon fruit juice production. The findings will contribute valuable insights for the development of an efficient and controlled vacuum concentration method for this exotic fruit's juice. Perhaps this is the first attempt to concentrate the dragon fruit juice since the area under the fruit is expanding fast and there is need to preserve the juice.