Enhancing the Efficacy of Microwave Blanching-cum-black Mould Inactivation of Whole Garlic (Allium sativum L.) Bulbs Using Ultrasound: Higher Inactivation of Peroxidase, Polyphenol Oxidase, and Aspergillus niger at Lower Processing Temperatures

Abstract

The freshly harvested whole garlic bulbs require the inactivation of peroxidase (POD), polyphenol oxidase (PPO), and Aspergillus niger . However, the conventional hot water blanching and modern pretreatment like ultrasound (US) and microwave (MW) cannot individually inactivate both the enzymes and Aspergillus niger to the desired levels without compromising the quality of the garlic due to either of the higher process temperatures (> 85 °C) or prolonged treatment times. Therefore, a two-stage sequential US followed by MW pretreatment for garlic bulbs was developed for simultaneous inactivation of POD, PPO, and Aspergillus niger to the desired levels and overcome the individual pretreatment drawbacks. The separate experiments were conducted for US and MW pretreatment using central composite design, and optimization was carried out using response surface methodology. When temperature constraint was considered during optimization, the US was able to reduce POD, PPO, and Aspergillus niger by 80.87%, 93.80%, and 2.60 logs, respectively, whereas MW reduced POD, PPO, and Aspergillus niger by 77.84%, 77.04%, and 1.90 logs, respectively. The US treatment (58.43 WL −1 ultrasound power density for 40 min with an initial bath temperature of 60 °C) followed by MW treatment (3 Wg −1 MW power density for 120 s) resulted in 90.37% POD and 92.38% PPO inactivation with 2.62 log reduction in Aspergillus niger . The maximum temperature reached in US + MW process was 83 °C which ensured no severe thermal damage to the garlic bulbs. The scanning electron microscopic images indicated that ultrasonication induced the porous structure in garlic and helped microwaves increase the product temperature rapidly and achieve the higher inactivation of enzymes and Aspergillus niger . Thus, the US was found to be enhancing the efficacy of the MW heating process.

Influence of ultrasound on the microbiological, physicochemical properties, and sensory quality of different varieties of pumpkin juice

“…The faster rate of POD inactivation compared to PPO inactivation indicates a higher resistance to ultrasound than that of PPO. This contrasts with the results reported by Kar and Sutar et al [ 46 ]. In Chen et al [ 24 ] who treated carrot juice with ultrasound, PPO activity decreased while POD activity increased, and PME activity showed an increase at 0.95 W/mL and a decrease at 2.38 W/mL and 3.80 W/mL.…”

Applications of ultrasonication on food enzyme inactivation- recent review report (2017–2022)

“… 100 mg/L sodium hypochlorite solution, US + NaOCl on PPO activity became predominant especially after day 4 of storage, leading to a 2.31–fold reduction at the end of storage. [98] 6 Lettuce ε-polylysine POD, PPO Probe US; 20 kHz, 17, 23, 29 W/L, for 10 min at 20 °C.ε-polylysine solution (0.1–0.6 g/L) At 12 days storage period, the least POD and PPO activity was observed for US - ε-polylysine treatment. [99] 7 Potato L-Cysteine PPO Ultrasonic bath; 28 kHz; 100–500 W; time 2–10 min; 20 °C.…”

“… [98] explored the combined effect of US and chlorine dioxide (ClO 2 ) on the enzyme activities of minimally processed bok choy and it was observed that different enzymes were affected differently by the combined US and ClO 2 treatment. To illustrate, the activity of PPO was observed to be reduced after 6–9 days of storage, before and after when the enzyme activity was increased whereas the POD activity showed a significant reduction throughout the storage period when compared to the control.…”

Exploring the Power of Thermosonication: A Comprehensive Review of Its Applications and Impact in the Food Industry

“…TS has the advantage of achieving a considerable level of enzyme inactivation while maintaining the nutritional and sensory attributes of food products. It can achieve this because it is a non-thermal processing method that requires lower temperatures than conventional thermal processing methods to inactivate enzymes [ 130 ]. Additionally, TS can reduce processing time and energy requirements, which can lead to cost savings and improved efficiency [ 122 ].…”