Hafizah Mohd Johar
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Preferred name
Hafizah Mohd Johar
Official Name
Hafizah, Mohd Johar
Alternative Name
Mohd Johar, H.
Johar, Hafizah Mohd
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Scopus Author ID
57194025640

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Mathematical modelling of moisture sorption isotherms by using BET and GAB models

2020-12-18 , Sriyana Abdullah , Keoh S.C. , Hafizah Mohd Johar , Norawanis Abdul Razak , Abd Razak Shaari , Rukunudin I.H.

Fish cracker is a popular local fish based snack in Malaysia. Besides the raw form which can be consumed directly, it is always eaten in the dried form. Thus study of moisture sorption isotherm of fish cracker is essential as to predict appropriate drying and storage conditions consecutively to enhance its nutrients, taste and aroma. In this study, the moisture sorption isotherms of fish crackers from two manufacturers M1 and M2 were developed by using a static gravimetric method at temperatures of 30, 40 and 50°C and water activity (aw) range of 0.04 to 0.80. It is a relationship between equilibrium moisture content (EMC) and aw at a specified temperature. The isotherms exhibited a sigmoid shaped which classified as type II in Brunauer-Emmett-Teller (BET) classification. The increase of temperature decreased the EMC of fish crackers while increase of aw increased the EMC. There was no significant difference of EMC between manufacturers M1 and M2. The moisture sorption isotherms of fish cracker were fitted into predicted isotherms by Guggenheim-Anderson-de Boer (GAB) and BET models. GAB model was found to be the best fit model of fish crackers' moisture sorption isotherms as compared to BET model.

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Effect of Process Variables on Gas Release from Free and Latex-Coated Calcium Alginate Beads

2024 , Yee-Ming Peh , Lee Boon Beng , Farizul Hafiz Kasim , Akmal Hadi Ma’Radzi , Sakthi Balaji , Ahmad Radi Wan Yaakub , Hafizah Mohd Johar , Mohd Asri Yusoff

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Microwave drying characteristics of Mas Cotek (Ficus deltoidea) leaves and its effects on colour and antioxidant properties

2017 , Hafizah Mohd Johar

Ficus deltoidea or locally known as Mas Cotek in Malaysia is one of the 10 prioritized herbs shortlisted by the government of Malaysia in its Economic Transformation Programme (ETP). The herb is rich in chemical constituents which are known to have diverse therapeutic potentials such as reducing level of sugar in blood, decreasing blood pressure, contracting the vagina after delivery, delaying menopause and reducing the risk of cancer. Ficus deltoidea is commonly consumed, stored and further processed in its dried form. High quality dried Ficus deltoidea leaves are therefore sought after by the end-users and drying is therefore the most effective method to remove moisture to preserve and extent the shelf-life of the herb. In this study, the thin layer microwave drying characteristics of Ficus deltoidea leaves were investigated and the corresponding quality of the dehydrated leaves such as the colour, total phenolic content and antioxidant properties, were evaluated with respect to the fresh leaves. Three microwave power levels (300, 600 and 800 W) and three ventilation rates (0.00, 0.013 and 0.025 m3/s) were the combination of drying parameters used to examine the drying characteristics and quality changes of dried Ficus deltoidea. A modified domestic microwave heater was used in the study. Microwave power levels were found to significantly (p < 0.05) affect the drying rate and the quality of the dehydrated Ficus deltoidea leaves. The drying rate increased as the microwave power level increased. The colour quality, total phenolic content and antioxidant properties were higher at the microwave power level of 600 and 800 W as compared to 300 W (p < 0.05) irrespective of ventilation rate. On the other hand, the effects of the ventilation rates on the drying rate and quality of dehydrated Ficus deltoidea leaves were found to be insignificant (p > 0.05) at all drying treatments. The thin layer drying characteristics of Ficus deltoidea leaves were evaluated and it was found that the drying took place in the falling rate period only. Five established thin layer drying models were used to compare the experimental and predicted drying kinetics by using statistical software analysis. Based on the fitting criteria, Midili et al. model appeared to best fit the thin layer microwave drying data. Finally, the assessment of sorption isotherm is crucial in order to ensure stability of the dehydrated Ficus deltoidea leaves during storage. Static gravimetric method was used to determine the moisture sorption isotherm (adsorption and desorption) of Ficus deltoidea leaves at two temperatures (5 and 30 °C) and five relative humidities ranged from 11.26 to 75.65 %. Five established isotherm models were used to compare the experimental and predicted sorption isotherms by using statistical software analysis. Based on the fitting criteria, Peleg model appeared to best fit the sorption isotherms data. The characteristic of the shape of the sorption curves were found to fall under the Type II category. As a conclusion, drying treatment of 600 W and 0.013 m3/s is suggested as drying conditions of Ficus deltoidea leaves for optimum dried leaves quality retention.

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Comparative study on mechanisms of gases release from Ca-alginate beads

2024 , Yee-Ming Peh , Lee Boon Beng , Farizul Hafiz Kasim , Akmal Hadi Ma’Radzi , Ahmad Radi Wan Yaakub , Hafizah Mohd Johar , D.F.A. Riza , N. Izza , K. Gustinasari , I.K. Maharsih , W.B. Sunarharum , M. Nurcholis , B.S.D. Dewanti , V.T. Widayanti , E. Mufidah , I. Qisthiya , D. Karadag , S. Idrus , H. Umakoshi , Y.C. Lee , D. Fatchurrahman , M. Zhu , K.A. Omwange , T. Addini

Calcium alginate (Ca-alginate) beads have attracted considerable attention as carriers for the controlled release of volatile compounds due to their biocompatibility and tunable properties. This study aimed to compare the release of ethylene and carbon dioxide gas from Ca-alginate beads. Ca-alginate beads were prepared from a sodium alginate solution containing ethephon and calcium carbonate as the gas-forming agent. The resulting solution was then extruded into a calcium chloride solution. The gas release behavior was studied by monitoring the concentration of released gases over time using gas detectors. Extrusion tip diameter, alginate concentration and gas-releasing agent concentration were systematically varied to assess their effect on the gas release rate. The results indicated distinct release patterns for ethylene and carbon dioxide gas. Ethylene gas exhibited a relatively slower and sustained release, while carbon dioxide gas exhibited a more rapid release. Moreover, the bead size influenced the gas release, with larger beads displaying faster release rates for ethylene and carbon dioxide gas. The concentration of alginate also played a role in modulating the release kinetics, with higher alginate concentration resulting in slower gas release. The findings have implications for designing and optimizing Ca-alginate-based systems for agricultural applications, including plant hormone delivery and modified atmosphere packaging.

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