Effects of tri‐frequency ultrasound‐ethanol pretreatment combined with infrared convection drying on the quality properties and drying characteristics of scallion stalk

Abstract

BACKGROUND Having short drying time and attractive product quality are important in fruit and vegetable dehydration processing. In this work, tri‐frequency (20, 40 and 60 kHz) ultrasound‐ethanol pretreatment, ultrasound‐water pretreatment and ethanol pretreatment were employed before infrared convection drying (ICD) of scallion stalks, which was aimed at improving the drying process and quality of the end products. The mass transfer, drying characteristics (moisture ratio and drying rate and quality properties of scallion (rehydration, color, flavor, optical microscope image, moisture distribution and microbiological quality) were analyzed. RESULTS All pretreatments have decreased the drying time by 33.34–83.34% compared to the control, while ultrasound‐ethanol pretreatment provided the highest time reduction (83.34%). The reason is that the volatility of ethanol have replaced air in the tissue, which produced a better osmotic dehydration effect and the cavitation effect of ultrasound changed the cell function of the material, so that the food tissue was rapidly compressed and expanded, resulting in damage to the cell structure. Ultrasonic‐ethanol pretreatment has greatly reduced the water loss and dry matter of fresh scallion, improved the rehydration effect of dried scallion, better retained the color and flavor of scallion and effectively reduced the microbiological quality of the scallion. CONCLUSION The tri‐frequency ultrasound‐ethanol pretreatment has effectively improved the drying process and quality characteristics of the dried scallion. Therefore, this research has a great contribution to the drying technology, as evident in the remarkable reduction in drying time and the improvement in the quality of the end product. © 2020 Society of Chemical Industry

Determination of drying characteristics, rehydration properties, and shrinkage ratio of convective dried melon slice with some pretreatments

“…On the other hand, a higher rehydration ratio was observed at higher ethanol concentration, higher citric acid concentration, and higher blanching temperature except higher US power ( p < .05). Similar reports were published by Doymaz (2014), Sahin and Doymaz (2017), Doymaz et al (2015), Doymaz and Sahin (2016), Doymaz and Bilici (2014), and Doymaz (2020) for citric acid and blanching pretreatments; Rojas et al (2020), Rojas et al (2020), Rojas et al (2018), and Zhou et al (2021) for ethanol pretreatment; Bozkır et al (2019) and Zhang et al (2016) for US pretreatment. Effect of citric acid and blanching on rehydration ability may be explained with more cell permeability and inactivation degradative enzymes.…”

“…Similarly, reduction in drying time in potatoes with ethanol pretreated was notified by Guedes et al (2021). Zhou et al (2021) reported higher DR in scallion stalk pretreated with ethanol solution.…”

“…was explained with more resistance to shrinkage by ethanol molecules entering to cell through osmosis byZhou et al (2021). In addition to this,Wang et al (2019),Tao et al (2019), andWu et al (2019) reported that the US pretreatment could enhance the rehydration ability of dried foods due to structural modifications such as pore, microchannels, larger tunnels, or spaces formation, and higher internal stress.…”

“…Hence, water in the food can be easily removed. Marangoni effect, which is based on the formation of a surface tension gradient between the ethanol and the food's water content, can significantly enhance the water transport (Llavata et al 2020; Zhou et al 2021).…”

Convective drying of cambuci, a native fruit from the Brazilian Atlantic Forest: Effect of pretreatments with ethanol and freezing

“…pretreated for 5-60 min)(Carvalho, Rojas, Silveira, & Augusto, 2020;Rojas & Augusto, 2018a, 2018b, apple (pretreated for 5 s to 30 min)(Amanor-Atiemoh et al, 2020;Rojas, Augusto, & Cárcel, 2020;Rojas, Augusto, & Cárcel, 2021;Zubernik, Dadan, Cichowska, & Witrowa-Rajchert, 2019), potato (pretreated for 3-15 min), carrot (pretreated for 5 s to 30 min)(Dadan & Nowacka, 2021;Santos, Guedes, Rojas, Carvalho, & Augusto, 2021), melon (pretreated for 10 min)(da Cunha et al, 2020), garlic (pretreated for 30 min)(Feng et al, 2019) and scallion stalk (pretreated for 5-30 min)(Wang et al, 2019;Zhou et al, 2020). On the other hand, and similarly to the present work, the ethanol pretreatment did not influence the drying process of pineapple pomace(Bitencourt, Carvalho, Corrêa, & Augusto, 2020), which was attributed to the sample structure and composition.…”