Effects of Heat and Ultra-sonic Processing on Some Qualities of Ma-Kiang (Cleistocalyx nervosum var. paniala) Juice

Abstract

Background and Objectives : Cleistocalyx nervosum var. paniala, commonly known as “Ma-Kiang” in Thai, belongs to the family Myrtaceae. This plant is a small to medium-sized tree found in tropical and subtropical regions, particularly in Southeast Asia. It has gained attention for its edible fruits and bioactive compounds, which are associated with various health benefits. Its fruits and extracts hold promise in health applications, particularly as natural antioxidants and anti-inflammatory agents. Ultra-sonic processing involves the use of high-frequency sound waves (20 kHz to several MHz) to generate intense pressure waves within a liquid medium. This technique has found significant applications in food processing, including fruit juice production, due to its ability to improve extraction, enhance flavor, and promote better preservation. The intense shear forces and heat generated during ultrasonication can also inactivate microorganisms (bacteria, yeasts, and molds) in fruit juices, improving the microbiological quality and extending shelf life. This, however, depends on the intensity, duration, and frequency of the ultrasound treatment. Ultra-sonic processing is considered another option for fruit juice processing, as it is a novel technology that can better preserve the bioactive compounds and antioxidant efficiency of the juice compared to heat processing. Therefore, this research aimed to investigate the effects of ultra-sonic processing on various qualities of Ma-Kiang juice compared to heat processing.

Methodology : To prepare Ma-Kiang juice, Ma-Kiang fruits were washed and drained, then refrigerated at 6ºC for 2 h before processing. The extraction of Ma-Kiang juice was done by extracting the Ma-Kiang fruits using a juicer, adjusting the total soluble solids (TSS) to 16ºBrix with fructose. Ma-Kiang juice was processed using a High Intensity Ultra-Sonic Processor with a frequency of 25 kHz and 20–80% amplitude for 30 min and heat treatment at 80ºC for 2 min, then immediately cool it by immersing it in an ice-water bath for 5 min. Store all processed samples at 4ºC before analyzing the quality. Physico-chemical qualities of the samples including color parameter, viz. L (brightness), a* (redness/greenness), b*(yellowness/blueness), C* (chroma) and total different colors (∆E), viscosity, total soluble solids, pH and total titratable acidity (TTA) were investigated. To study the health benefits, total anthocyanin content, total phenolic compounds, and antioxidant capacity, viz.  2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity, ferric-reducing antioxidant power (FRAP), and 2,2’-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS⁺) radical scavenging activity were assessed. Polyphenol oxidase (PPO) and peroxidase activity in the samples were monitored, and the residual of both enzymes were also calculated. For safety consumption, indicator microorganisms, according to the Thai Community Product Standard for Ma-Kiang juice (TCPS. 484/2014), viz. total plate counts, yeasts and molds, coliform bacteria, Escherichia coli, Salmonella, Staphylococcus aureus, Bacillus cereus and Clostridium perfringens, were determined.

Main Results : From the experimental results, it was found that the brightness value (L) of the processed tamarind juice decreased after being treated with heat and high-frequency sound waves compared to fresh tamarind juice (control). It is evident that as the intensity level of the sound waves increases, the color value L significantly decreases. The heat-processed tamarind juice had the lowest redness value (a*) and the highest yellowness value (b*). For samples processed with high-frequency sound waves, the a* and b* values tended to increase with the intensity of the sound waves, which correlated with the color intensity (C*) and total color difference (∆E) values in the samples. The viscosity, total soluble solids, pH, and total titratable acidity of the processed Ma-Kiang juice using heat and ultra-sonic processing at different frequency attitude levels showed no statistically significant differences when compared to the unprocessed samples. Samples processed with ultrasonication still retained high levels of bioactive compounds (total anthocyanins and total phenolic compounds) and antioxidant capacity (DPPH, FRAP, and ABTS^•+ assays) compared to fresh samples, and they contained more than that processed by heat. The activities of polyphenol oxidase and peroxidase in the samples decreased after processing. Additionally, it was found that heat processing at a temperature of 80ºC for 2 min and ultrasonication at an intensity level of 80% could inhibit indicator microorganisms related to the sanitation and safety consumption of Ma-Kiang juice, bringing their numbers below the standards set by the Thai Community Product Standard (TCPS. 484/2014).

Conclusions : From this research, it can be concluded that processing Ma-Kiang juice with ultra-sonic processing at kHz, with an intensity level of 80% for 20 minutes, was the most optimal condition. This method can better preserve various qualities and bioactive compounds, as well as the antioxidant efficiency of the product, compared to processing under other conditions. Additionally, it can be suggested that ultra-sonic processing was another option for fruit juice processing and can be commercially utilized. For future research, sensory evaluation may be required before the technology is further developed industrially, and the effects of ultra-sonic processing on the shelf life and other bioactive compounds in Ma-Kiang juice should also be studied.