Sze Pheng Ong

Drying Kinetics and Antioxidant Phytochemicals Retention of Salak Fruit under Different Drying and Pretreatment Conditions

Kinetics of hot air drying and heat pump drying were studied by performing various drying trials on salak slices. Isothermal drying trials were conducted in hot air drying and heat pump drying at a temperature range of 40–90°C and 26–37°C, respectively. Intermittent drying trials were carried out in heat pump drying with two different modes: periodic heat air flow supply and step-up air temperature. It was observed that the effects of relative humidity and air velocity on drying rate were significant when moisture content in salak slices was high, whereas the effects of temperature prevailed when the moisture content was low. As such, it was proposed that drying conditions should be manipulated according to the moisture transport mechanisms at different stages of drying in order to optimize the intermittent drying and improve the product quality. Generally, loss of ascorbic acid during drying was attributed to thermal degradation and enzymatic oxidation, whereas the loss of phenolic compounds was mainly due to thermal degradation. Experimental results showed that heat pump drying with low-temperature dehumidified air not only enhanced the drying kinetics but produced a stable final product. Heat pump–dried samples retained a high concentration of ascorbic acid and total phenolic compounds when an appropriate drying mode was selected.

Microstructure and Optical Properties of Salak Fruit Under Different Drying and Pretreatment Conditions

The effect of heat treatment on microstructural and optical properties of salak fruit was investigated. Blanching pretreatments were performed at three temperatures (50–70°C) and drying experiments were conducted by using a hot air dryer (40–90°C), a heat pump–assisted dryer (constant and intermittent modes, 26 and 37°C), and a freeze dryer. The microstructure of the sample was examined with scanning electron microscopy (SEM) and the color change was assessed based on total color change value (ΔE*). In general, the freeze-dried product showed a porous structure and the hot air–dried product had a dense structure. Heat pump–assisted drying (both constant and intermittent modes) can maintain the original shape of parenchyma cells better compared to other drying methods, where the cells remained intact and showed less wrinkling after drying. However, pretreatment had an adverse effect on the products microstructure. It was observed that elongation and disruption of parenchyma cells increased significantly with blanching temperature. On the other hand, browning indices were different among the samples depending on the pretreatment and drying conditions. Heat pump–assisted drying in constant mode can not only can prevent a high browning rate during drying but minimizes and delays color degradation during storage.

Optimization of Heat Pump–Assisted Intermittent Drying

In the present study, heat pump–assisted drying of salak fruit was optimized by dividing the dehydration process into three distinct phases, namely, the initial, intermittent, and final stages. Drying variables considered for the optimization were the intermittent duration (X 1), intermittent ratio (X 2), and intermittent cycle (X 3); the response variables studied were the total drying time (Y 1), total heating time during intermittent drying (Y 2), total heating time after intermittent drying (Y 3), total color change (Y 4), ascorbic acid content (Y 5), and total phenolic content (Y 6). Response surface methodology was used to determine the best combination of the drying variables that could provide the shortest drying period and premium product quality. Experimental results showed that all of the response variables were improved under the optimized intermittent drying conditions compared to the conventional method using constant drying conditions. The optimized heat pump–assisted intermittent drying reduced the drying time by 36% and improved phytochemicals retention with ascorbic acid and total phenolic content recorded at 18.4 ± 1.8 mg ascorbic acid/100 g dw and 43.3 ± 2.2 mg gallic acid equivalent (GAE)/g dw, respectively. The color change of the final product was minimum with a ΔE* value of 7.26 ± 2.03.

Drying characteristics of Orthosiphon stamineus Benth by solar-assisted heat pump drying

ABSTRACT Processing methods of Misai Kucing still remain crude and lack technological advancements. In terms of drying, very few studies have attempted to apply advanced drying technology to improve Misai Kucing quality and drying time. This paper presents first attempt to improve Misai Kucing drying kinetics and product quality through solar-assisted heat pump drying and comparison was made against solar drying. Experimental results showed that solar-dried samples had the greatest total color change and loss of two bioactive ingredients as compared to solar-assisted heat pump-dried samples due to its longer time process, higher drying temperature, and chlorophyll degradation. By comparing the statistical values, it showed that the Page model had the best goodness of fit at all tested dried samples by both drying methods.

Effect of ambient conditions on drying of herbs in solar greenhouse dryer with integrated heat pump

ABSTRACT An even span solar greenhouse dryer was built and applied to dry Java tea (Orthosiphon aristatus) and Sabah snake grass (Clinacanthus nutans Lindau). Findings showed that the solar greenhouse dryer performs satisfactorily during clear weather except at nighttime and rainy day due to product rehydration which is heavily influenced by high relative humidity from ambient air. Integrating of heat pump into the solar greenhouse dryer has successfully reduced the room relative humidity by 10–15%. Also, heat pump has mitigated the product rehydration issue by maintaining room relative humidity at maximum of 65% throughout the drying period. The drying rate of Java tea was improved three to fourfold, i.e., from 0.004–0.008 to 0.018–0.025 g H2O/g DM min, whereas 10% of drying time was saved for both Java tea leaf and Sabah snake grass leaf with the assistance of heat pump system. Meanwhile, the supply of dry air from the heat pump system with a magnitude of 0.25–0.50 m/s helps in enhancing the drying rate of the herbs as well as minimizing the nonuniformity of drying temperature and relative humidity inside the solar greenhouse dryer.

Convective Air Drying of Raw and Cooked Chicken Meats

This research investigated the effects of convective air drying on the quality of raw and cooked chicken breast meats at 60, 70, and 80°C. Raw samples were cut into sizes of 20 mm × 20 mm × 7 mm and cooked samples were precooked in hot water and cut into similar sizes. It was observed that cooked samples had a lower initial moisture content and dried faster than the raw samples. The thicknesses of raw samples were observed to increase in the first 2 h due to internal water vapor generation. The rigid structure of the cooked samples resulted in a lower degree of shrinkage compared to the raw samples. Rehydration capacity was lower in the cooked samples, which could be due to the rigid structure resulting from the precooking process. This further reduced the imbibition of water into the sample. Effective diffusivity values were determined in the order of magnitude of 10−11 m2/s and comparable to those from the literature. Hardness values of dried cooked samples were significantly higher (p < 0.05) than the dried raw samples, whereas elasticity was significantly lower (p < 0.05).

Kinetic retention of sialic acid and antioxidants in Malaysian edible bird’s nest during low-temperature drying

ABSTRACT Drying is one of the essential processing steps for dried edible bird’s nest; however, sialic acid and antioxidant can be highly thermosensitive and unstable. Therefore, aim of this study was to determine the degradation kinetics of sialic acid and antioxidants during low-temperature drying at 25–40°C as compared to conventional hot air-drying at 70°C. These compounds’ degradation exhibited first-order kinetics. Sialic acid and antioxidant retentions were 83.9 and 96.6%, respectively, at 25°C, and 78.7 and 91.5% at 40°C, respectively, by low-temperature drying; while, 42.5 and 38.7%, respectively, at 70°C by conventional hot air-drying. Finally, empirical models were significantly fitted to predict sialic acid and antioxidant retention as edible bird’s nest reached a certain level of drying, which may be useful from the processing standpoint and validate the usage of low-temperature drying as a process tool for retention of sialic acid and antioxidant in edible bird’s nest.

Clinacanthus nutans Lindau: Effects of drying methods on the bioactive compounds, color characteristics, and water activity

ABSTRACT The application of solar drying (SD) and heat pump-assisted solar drying (HPSD) on the retention of flavonoid components, total color changes, and water activity of Clinacanthus nutans Lindau leaves were investigated. Analysis of data shows significantly higher extractable yield and flavonoid (orientin and vitexin) percentage during the drying with HPSD. The same drying technique also revealed optimum color values and low water activity. Thin-layer models fitted to the experimental data show that Hii and Law model is suitable for SD, while logarithmic model is able to give a good fit to HPSD.

Color changes, nitrite content, and rehydration capacity of edible bird's nest by advanced drying method

ABSTRACT This article presents the authors’ first attempt to improve quality of edible bird’s nest through continuous and intermittent low-temperature drying (25 and 40°C) with infrared and ultraviolet C (UVC) treatments. The attributes of quality were compared in regard to quality of hot-air-dried samples at 70–90°C. Experimental results showed that a significant improvement in the quality of edible bird’s nest in terms of minimizing color changes and rehydration capacity using intermittent low-temperature drying with infrared and UVC drying profile. However, it was also found that any drying method has less significant effect on the nitrite content of edible bird’s nest.

Conference Report: The 2nd International Symposium on Processing and Drying of Foods, Vegetables and Fruits, June 18–19, 2012, University of Nottingham, Malaysia Campus, Semenyih, Selangor, Malaysia

The 2nd International Symposium on Processing and Drying of Foods, Vegetables and Fruits (ISPDFVF 2012) was successfully organized by the Center for Food and Bio-products Processing and The Faculty of Engineering, University of Nottingham, Malaysia Campus (UNMC) from June 18–19, 2012. The International Advisory Board was chaired by Professor Arun S. Mujumdar (Minerals, Metals, and Materials Technology Center, National University of Singapore, Singapore) and co-chaired by Ir Professor Law Chung Lim (UNMC) while the Local Organizing Committee was chaired by Dr. Hii Ching Lik (UNMC) and co-chaired by Dr. Ong Sze Pheng (UNMC). The first symposium was held last year in the UNMC Kuala Lumpur Teaching Center (April 11–12, 2011).