Drying Kinetics, Physicochemical and Thermal Analysis of Onion Puree Dried Using a Refractance Window Dryer

Abstract

Onions have a high moisture content, which makes them more susceptible to microbial growth. Drying is one of the postharvest preservation methods applied to decrease onion moisture content, thereby increasing its storage life. In this study, onions were peeled, washed, cut into quarters, hot water blanched, and pureed. The puree was further dried using two different drying methods: refractance window drying (RWD) (water temperature: 70 °C) and convective drying (CD) (50 °C). The puree was spread on prefabricated trays at varying thicknesses of 2 mm, 4 mm, and 6 mm. It was observed that, irrespective of the drying method, moisture ratio (MR) decreased and drying time and effective moisture diffusivity increased with respect to the thickness of the puree. In addition, the Lewis model and the Wang and Singh model showed the highest R2 and lowest SEE value for RWD and CD, respectively. Moreover, the MR of onion puree during RWD and CD was predicted using a multi-layer feed-forward (MLF) artificial neural network (ANN) with a back-propagation algorithm. The result showed that the ANN model with 12 and 18 neurons in the hidden layer could predict the MR, with a high R2 value for RWD and CD, respectively. The results also showed that the thickness of the puree and drying method significantly affected the physicochemical quality (color characteristics, pyruvic acid content, total phenolic content, total flavonoid content, antioxidant capacity, and hygroscopicity) of onion powder. It was concluded that RWD proved to be a better drying method than CD in terms of the quality of dried powder and reduced drying time. Irrespective of the drying method, 2 mm-thick puree dried yielded the best-dried onion powder in terms of physicochemical quality, as well yielding the lowest drying time. These samples were further analyzed for calculating the glass transition temperature.

Refractance Window Drying as an Alternative Method for Brewer’s Spent Grain Preservation

“…Compared to conventional methods such as convective and freezedrying, RW drying boasts shorter processing times and higher energy efficiency [19,22,23]. The refractance window technique has demonstrated success in processing a diverse range of biomaterials, including tomatoes [22], strawberries [24], carrots [24], mangoes [25], açaí [26], guavas [27], passion fruit [28], bananas [29], onion [30], apples [31], and even unconventional items like yogurt [32] and microalgae [33].…”

Development of a Low-Cost Artificial Vision System as an Alternative for the Automatic Classification of Persian Lemon: Prototype Test Simulation

“…In this sense, recent research has focused on proposing solutions based on the use of artificial vision and machine learning to solve this type of problem [3]. Through the use of artificial intelligence, such as the implementation of artificial neural networks, it has been possible to evaluate complex systems for the prediction and control of different areas in the food industry, such as extrusion [4], process conditions (formulations) [5], drying [6], or evaluating its functional content [7]. In the last few years, artificial neural networks have proven to be advantageous because they allow the evaluation of complex and multivariable systems, thus providing an indicator that demonstrates the quality of a product.…”

Convective drying of sweet pepper (Capsicum annuum L. 'Tres Cantos') and yellow onion (Allium cepa L. 'Yellow Granex F1')

“…In recent years, research efforts have been directed towards investigating the drying characteristics of various fruits and vegetables, mostly concerning process parameters and the development of mathematical models. For instance, Zalpouri et al (2023) reported the drying of onion (Allium cepa L. 'Punjab Naroya') puree using two different drying methods (refractance window drying and convective drying). It was observed that irrespective of the drying method, the moisture ratio decreased, and drying time and effective moisture diffusivity increased with the thickness of the onion puree.…”