Abstract
In most cases, conventional drying produces inferior quality products and requires higher drying times. A continuous pilot Refractance Window® equipment was used to dry Aloe vera gel slabs of 5 and 10 mm thick at 60, 70, 80, and 90 °C, seeking a dry product with high-quality retention. Based on five empirical models, drying kinetics, diffusion coefficient, and activation energy were analyzed. Midilli–Kuck was the best predicting model. Short drying times (55–270 min) were needed to reach 0.10 g water/g solid. In addition, the technique yielded samples with high rehydration capacity (24–29 g water/g solid); high retention of color (∆E, 3.74–4.39); relatively low losses of vitamin C (37–59%) and vitamin E (28–37%). Regardless of the condition of temperature and sample thickness, a high-quality dried Aloe vera gel could be obtained. Compared with other methods, Refractance Window® drying of Aloe vera achieved shorter drying times with higher quality retention in terms of color, vitamins C and E, and rehydration. Finally, the dried Aloe vera gel could be reconstituted to a gel close to its fresh state by rehydration.
Highlights
The Aloe vera plant is native to Africa, it is cultivated worldwide in most tropical and subtropical regions due to its ability to adapt to different climates [1]
The cost of an Refractance Window® (RW) equipment is approximately one-third to one-half of that of a freeze dryer to dry a similar amount of product, while the energy costs to operate RW dryers are less than half of freeze dryers [8,23]. This is an important consideration, since RW has demonstrated the capability to produce dried products of similar quality to those obtained by freeze-drying [34]
When comparing the results of this work with other methods used to dry Aloe vera gel and puree reported in the literature, it was observed that by using Refractance Window® drying, significantly shorter drying times were obtained with higher quality retention in terms of color, vitamins C and E, and rehydration
Summary
The Aloe vera plant is native to Africa, it is cultivated worldwide in most tropical and subtropical regions due to its ability to adapt to different climates [1]. The clear inner gel contains most of the bioactive components such as flavonoids, terpenoids, lectins, fatty acids, anthraquinones, monoand polysaccharides (pectins, hemicelluloses, glucomannan), tannins, sterols (campesterol, β-sitosterol), enzymes, salicylic acid, minerals (calcium, chromium, copper, iron, magnesium, manganese, potassium, phosphorus, sodium, and zinc), and vitamins (A, C, E, β-carotene, B1, B2, B3, B6, choline, B12, folic acid) [2]. This gel has moisture ranging from 99.0 to 99.5% (wet basis, wb) and 0.5% wb to 1.0% wb dry matter [3]. The main reason for this growth may be related to rising health-consciousness, since consumers prefer products containing natural ingredients (such as aloe gel), which are perceived to be safer and healthier than their processed or chemical counterparts [6]
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