Effect of multi‐frequency countercurrent ultrasound treatment on extraction optimization, functional and structural properties of protein isolates from Walnut (Juglans regiaL.) meal

Abstract

This study evaluated the effects of ultrasound treatment on walnut meal protein (WMP) extraction and techno‐functional properties. The Box‐Behnken Design (BBD) was adopted for the optimization of the traditional and ultrasound‐assisted extraction (UAE) processes. Standard protocols were used to assay the techno‐functional characteristics. The extraction models’ statistical results exhibited adequacy with the least desirability index of 95.8%. The UAE enhanced the WMP extraction yield, purity, and chemical score by 30.15%, 16.27%, and 9.74%, respectively, while reducing the extraction time by 25% over the control. The emulsion and foam stabilities and bulk density increased by 34.5%, 39.8%, and 6.1%, respectively, over the control. The α‐helix decreased while β‐sheet, β‐turns and random coil secondary structure components increased significantly (p < .05) by 95.76%, 101.3%, 105.1%, and 85.7% correspondingly. The dual‐frequency combination (20/40 kHz/kHz) was the best frequency mode. WMP could serve as a functional additive in manufactured foods as texture and flavor enhancer. Practical applications Walnut meal protein (WMP) has a well‐balanced amino acid profile and its economic use could be practically increased as a food ingredient by ultrasound‐assisted extraction. By this technique, WMP could be employed for the development of enhanced food ingredients rather than being discarded as animal feed. This study showed a positive effect of ultrasonic‐assisted alkaline pretreatment on WMP extraction, functionality and structure characteristics. In addition to process improvement, ultrasound is energy efficient and environmentally friendly. Therefore, the applicability of this technique to improve the functionality of plant proteins from industrial by‐products to be included in food products is promising.

Extraction of phenolics and anthocyanins from purple eggplant peels by multi-frequency ultrasound: Effects of different extraction factors and optimization using uniform design

“…Naa Yarley et al [25] also found that the polysaccharides yield from crude sorghum leaf with multi-frequency ultrasound increased by 26.69 %. Moreover, a large number of similar results have been reported under the use of multi-frequency ultrasound in recent years [26] , [27] , [28] , [29] , [30] , [31] . For the extraction of phenolic compounds from eggplant, although several studies have been performed by ultrasound [32] , [33] , [34] , [35] , there are very few works for describing the extraction process using multi-frequency ultrasound, as well as rarely exploring to optimize the extraction variables via uniform design approach.…”

Impact of ultrasound processing on alternative protein systems: Protein extraction, nutritional effects and associated challenges

“…Combining two or more frequencies in a single US system provides certain advantages due to the interaction between different US waves [59] as the combined influence of all the frequencies is higher than the effect of the sum of the individual frequencies [51] , resulting in a significant increase in cavitation yield [60] . Pre-treatments using dual frequency of 20/40 kHz in a combined working mode and pulse on and off-time of 5 and 2 s respectively, was carried out in a specially designed equipment comprising of controllers, two probes, a temperature regulating system, a reaction vessel, and a liquid circulating system ( Fig.…”

“…Moreover, these treatments also achieved higher soluble protein contents compared to other treatments using the same frequency at other angles, with levels of 16.07 % higher soluble proteins compared to treatments at 40 + 20 kHz 0° and 19.02 % higher than those at 40 + 20 kHz 30° [44] . Multi frequency US models have also been effectively used for protein extraction from walnut meal [59] and the microalgae Chlorella pyrenoidosa [62] .

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“…Apart from using water and alkali as solvents for protein extraction, few studies have employed other solvents, such as Tris HCl buffer, ethanol, sodium phosphate buffer for UAE from moringa leaves [95] , walnut meal [59] and Arthrospira platensis [96] , respectively. Universally, the solvent should be judiciously selected so that, apart from being non-toxic, it has low vapour pressure, viscosity, and surface tension to facilitate high-intensity cavitation [46] .…”

Multi-mode S-type ultrasound-assisted protein extraction from walnut dregs and in situ real-time process monitoring

“…Protein extraction is considered an effective method to improve the comprehensive utilization and economic value of walnut dregs. As a conventional method to extract proteins, alkali-soluble extraction has been extensively applied in protein extraction due to its advantages of operational simplicity and cost-effectiveness [7] . However, alkali-soluble extraction has some shortfalls, including large solvent consumption, low extraction efficiency, and high energy consumption [8] .…”