Abstract

Shallot is one of the most consumed commodities in Indonesia, but shallot undergo quality deterioration due to metabolic process and microbial growth. Turning shallots into a paste is a practical method for minimal processing. Therefore, this research was done for extend the duration of its shelf life using hypoiodous acid or HIO which was known as preservative. Hypoiodous acid is an oxyacid that acts as antimicrobial agent. As much as 0,2 mM HIO solution in water was prepared for soaking process of shallot while soaking in pure water was also conducted for producing control. Shallot paste was produced after dried for 3 hours and followed by packing in sealed-ziplock. Fifteen minutes steaming was then applied prior to storage in room temperature. Value of pH, total dissolved solid (TDS), L*, and browning index was analyzed descriptively based on the graph for each three days measurements. As result, HIO treatment stabilized the decrease of pH ranging from 6.6 to 6.2 after 30 days of storage while HIO hindered the increase in TDS even though until half of storage duration. All value of L* for both and HIO treatment showed a decrease starting from 45 to 17 but less decrease on its value was found in HIO treated shallot paste while browning index was also found as similar trends. As conclusion, HIO treatment might stabilized the change in pH, TDS, L*, and browning index. This research might open the knowledge of potent use of HIO in extension of shallot storage.

1. Introduction

Shallot is one of the most commonly consumed commodity in Indonesia. Unfortunately, shallot could experience quality decreases due to metabolic process and microbial growth such as mold ¹. Up until now, preservation of shallot has always been done by salting, drying, pickling, and preserving them with acid. These preservation methods alter shallot’s taste and require a lot of process. Further processing of shallot by turning shallot into shallot paste is a way to minimally process shallot and make it practical. But in spite of that, processing shallot into shallot paste without further treatment will reduce the quality and also shallot paste’s shelf life. It is known that shallot paste can only last for 12 days during storage ². Therefore, further treatment is needed to extend its shelf life.

Hypoiodous acid is an oxyacid resulting from the combination of hydrogen peroxide (H₂O₂) and potassium iodate (KIO₃). This reaction begins with the activation of the peroxidase enzyme by H₂O₂ and when it is active, the peroxidase enzyme then oxidizes IO₃ to HIO ³. Pretreatment technology using HIO has been proved to be potentially good in maintaining the quality of some food products, such as red chili paste (Capsicum annum L.), apple (Malus domestica), and snake fruit (Salacca edulis reinw.). HIO managed to inhibit microbial and chemical activities because HIO has potent microbicidal activity against bacteria ⁴. In addition to giving shallot paste the HIO pretreatment, drying method is also able to extend shallot paste’s shelf life. Drying method will reduce the water content to a certain extent and suppress biological reactions and microbial growth of shallot paste ⁵. Therefore, combining both HIO pretreatment and drying method could be able to extend shallot paste’s shelf life better.

Physicochemical properties are an important factor to decide the quality of food products, including shallot paste. Changes in physicochemical properties could be a sign of decrease in shallot paste quality. The use of HIO pretreatment and drying method combination is expected to maintain shallot paste’s physicochemical properties. Research on fresh shallots with ozone treatment has been done, but research on HIO treatment on shallot paste has never been done before. Based on those considerations, this study aims to identify the effect of HIO pretreatment and drying method combination on pH value, total dissolved solids, lightness, and browning index of shallot paste during storage.

2. Material and Method

This research was done from July until October 2022 in Center of Research and Services Diponegoro University, Semarang, Indonesia. The sample used were shallots (Allium cepa L. var. aggregatum) obtained from a local grocery store. The selection was conducted using a previous research method ⁶. Fresh and unblemished shallot, weighing between 6 and 8 g and averaging around 7 g, were purchased from a local grocery store that had distance about 2 kilometers from the research station. Shallot selection was conducted also using size criteria of about 3 to 5 cm wide in size. Other materials used in this research were hydrogen peroxide (Merck, Germany), KI (Merck, Germany), and chopper (Philips HR 1661, Hungary), continuous band sealer (FRB 770, Indonesia) oven (Corona DHG-9030A, Indonesia), analytical scale (Fujitsu FSR-A 200, Japan), pH meter (pH Meter 6-in-1 Pentype Tester, Taiwan), colorimeter (CHNSpec CS-10, China).

The purchased shallots were then transferred to the research station with an aseptic container. Afterwards, the shallots were immediately given further treatment without any restorage.

The preparation of HIO was conducted using previous research ⁷ with modification. As much as 20 mM hydrogen peroxide (H₂O₂) and 20 mM potassium iodide (KI) was mixed in the similar volume to create a chemical reaction into HIO solution. The chemical reaction among this two substances generated HIO after 6 minutes reaction time as the following reaction:

I^-_(aq) + H₂O₂ ⥦ HIO + OH^-

I_{2 (aq)} + H₂O ⥦ HIO + I^-_(aq) + H⁺

5HIO ⥦ HIO₃ + 2I₂ + 2H₂O

The solution was then used for soaking process for 6 minutes. The solution could only be used for one time soaking. The drying process was done with a drying oven with air flow for 3 hours at 60^oC. Finally, shallot was prepared for packing and preservation.

Shallots chopped using a chopper then put into retort pouches. The retort pouches filled with shallots paste were sealed using a continuous band sealer then steamed for 15 minutes. The steamed shallot was soaked in water to cool down the temperature and then stored at room temperature (27^oC).

Application of HIO on shallot referred to previous research ⁸ with modification. HIO treatments were done by soaking samples in 0.2 mM HIO solution for 15 minutes. The samples were then drained and dried out with air circulation. Shallots with control and HIO treatment ready to be given the next treatment, which was drying.

Drying on shallot was conducted using method by previous researcher ⁹ with modification. Shallots were cut into thin circular shape using knife, then put evenly distributed onto each tray, based on the treatment. Both shallots were put in the heating drying oven at 60oC for 3 hours. After drying process, each samples chopped finely for around 2 minutes, then packed as much as 20 grams with 10x6 cm sealed-ziplock. Shallot paste in retort pouch was steamed in hot air for about 15 minutes. Shallot paste was stored at room temperature. Parameter analysis was done every 3 days for a month.

Color changes determination referred to other researcher ¹⁰ using colorimeter method. Color data presented as L*a*b* value. Colorimeter was calibrated with standard black and white plates as provided by manufacturer. The value of browning index was then calculated using following formula:

(1)

(2)

The value of pH analysis referred to previous researcher ¹¹, using pH meter with modification. pH meter was calibrated with buffer solution at pH 4 and 7. Sample was extracted by dissolving 2 g of sample in 10 ml water and then extracted with filter cloth. Value of pH was analyzed by dipping the pH meter probe into the sample extract.

Total dissolved solid (TDS) analysis referred to previous reseacher ¹², with portable TDS meter. Each samples were prepared as much as 2 g, then dissolved into 10 ml of aquadest. Samples were extracted with filter cloth. The analysis was carried out by dipping the probe of portable TDS meter into the sample.

The characteristic of shallot paste was evaluated for 30 days. During this period, the shallot samples were evaluated every 3 days for quality characteristics using some of the methods described earlier. The shallot pastes were stored at room temperature.

Data analysis of color changes determination, pH analysis, TDS analysis and pH change in shallot was measured using Microsoft Excel 2019 then presented in a graph with error bars and scattered line.

3. Result and Discussion

Based on Figure 1, pH value of HIO-treatment shallot was more stable than control, resulting the range between 6.1 to 6.5. HIO has been known to inhibit browning reaction and pH reduction in fruit, such as snake fruit ¹³. HIO is a compound that might inhibit bacterial and microbial growth, which can result in quality damage of shallot ¹⁴. Shallot also contains antimicrobial properties, such as allicin. Allicin actively inhibits a wide range of gram-positive and gram-negative bacteria ¹⁵. Combination of allicin and HIO as antimicrobial substances may preserve the quality of shallot for a long time. The more pH value reduction happens mean the higher acidity of shallot. Besides bacterial and microbial growth, quality damage of shallot can also be affected by metabolic reactions rate, so that in storage for several days, shallot’s pH value will be decreasing.

Based on Figure 2, total dissolved solids (TDS) of shallot with HIO treatment undergo steady increasing than control sample. This may happen because sample with HIO treatment contains more ion than the control sample. Hypoiodous acid contains several ions such as iodide and hydrogen ion ¹⁶. Rich concentration of ions in shallot can be attributed to its ability to ionize easily ¹⁷. Ionic concentration is part of the conductivity measurement. Conductivity properties related to dissolve solutes. The higher ion concentrated in shallot means it contains lot of dissolved solids.

Based on Figure 3, the L* value of shallot paste with HIO treatment and control treatment decreased during storage. Shallot paste with HIO treatment in lower temperature has a highest L* value while shallot paste with control treatment in room storage has a lowest L* value. Shallot paste with HIO treatment have a higher L* value than shallot paste with control treatment. HIO treatment could slow down the decrease in L* value. HIO is a compound that can inhibit browning enzyme so the decrease in L* value was lower than without HIO ¹⁸. Shallot paste in room temperature had higher L* value than those of low temperature. Storage temperature affect the rate of browning reaction. Higher storage temperature cause a greater decreased in shallot L* value ¹⁹.

Browning index of shallot with control pretreatment was higher and more unstable than sample with HIO pretreatment (Figure 4). Anthocyanin pigments and chlorogenic acid in shallots undergo a browning reaction which causes a change in the color of the shallot paste. Anthocyanin and chlorogenic acid in onions may undergo oxidation reaction with the polyphenol oxidase enzyme to produce melanoidin which gives a brown color ²⁰. This browning reaction runs faster at higher temperatures.

4. Conclusion

Based on this research, it can be concluded that shallot paste with HIO pretreatment was more stable in pH value, TDS value, L* value, and browning index than those of control. This stability proved the benefit of HIO as preservative substance as it could preventing browning and acidity on shallot.

References