Novel isochoric impregnation to develop high-quality and nutritionally fortified plant materials (apples and sweet potatoes)

Authors: Bilbao-Sainz, Cristina; Chiou, Bor-Sen; Takeoka, Gary; Williams, Tina; Wood, Delilah - De; POWELL-PALM, MATTHEW - University Of California Berkeley; RUBINSKY, BORIS - University Of California Berkeley; McHugh, Tara

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2022
Publication Date: 10/1/2022
Citation: Bilbao-Sainz, C., Chiou, B., Takeoka, G.R., Williams, T.G., Wood, D.F., Powell-Palm, M., Rubinsky, B., McHugh, T.H. 2022. Novel isochoric impregnation to develop high-quality and nutritionally fortified plant materials (apples and sweet potatoes). Journal of Food Science. 87(11):4796-4807. https://doi.org/10.1111/1750-3841.16332.
DOI: https://doi.org/10.1111/1750-3841.16332

Interpretive Summary: Functional foods can be conventional foods if they contain naturally occurring bioactive substances that improve well-being and health, reduce disease risk and/or improve disease outcomes. Functional foods can also be produced by fortification with desirable bioactive compounds, such as vitamins, minerals, beneficial antioxidants or probiotic bacteria. In this manuscript, we evaluated isochoric impregnation as a potential novel technology to infuse bioactive compounds into solid foods for the development of fortified functional food products during isochoric freezing preservation. We examined the effectiveness of isochoric impregnation on the fortification of Beauregard sweet potatoes and Granny Smith apples with ascorbic acid. We found that when the potatoes and apples are immersed in a solution containing ascorbic acid, the hydrostatic pressure generated during isochoric freezing caused the infusion of the ascorbic acid into the pores of the sweet potatoes and apples. Isochoric impregnation at -3 °C increased ascorbic acid contents up to 516 mg/100g for apples and up to 382 mg/100g for sweet potatoes. The isochoric impregnated apples and sweet potatoes had similar textures to fresh samples since the cellular tissues were well preserved. Also, isochoric impregnation preserved samples from browning, but samples appeared translucent due to the infusion of the sucrose/ascorbic acid solution into the pores of the cellular tissue.

Technical Abstract: Isochoric impregnation was explored as a novel pressure-assisted infusion technique to fortify plant materials (apple and sweet potatoes) with bioactive compounds (ascorbic acid). Apple and potato cylinders were impregnated with a sucrose solution containing 4% ascorbic acid (AA) while freezing under isochoric conditions. Isochoric impregnation resulted in greater infusion of AA compared to infusion at atmospheric pressure, which demonstrated the feasibility of this impregnation technology. Processing temperatures (-3°C and -5°C) and processing times (1, 3 and 5 hours) significantly affected the ascorbic acid infusion. The AA content values ranged from 446 to 516 mg/100g for apples and 322 to 831 mg/100 g for sweet potatoes under isochoric conditions, whereas the maximum AA contents for infused apples and sweet potatoes at atmospheric pressures were 18 mg/100g and 241 mg/100g, respectively. For both plant materials, isochoric impregnation at -3°C did not cause major changes in texture and microstructure of the biological tissues. These results indicated that isochoric impregnation of solid foods could be a feasible technology for infusion of bioactive compounds without significantly altering its matrix. The findings of this study showed that the use of isochoric impregnation as a fortification technique is a promising way to develop fresh-like and value-added products with improved nutrition during preservation at subfreezing temperatures.