Efficient drying of laser-treated raspberry in a pulse-spouted microwave freeze dryer

Abstract

Pulse-spouted microwave freeze drying (PSMFD) has been shown to be more energy efficient than the conventional vacuum freeze dryer. PSMFD yields higher drying rate and better energy efficiency due to volumetric heating. Because of the mass transfer resistance due to the berry’s epidermal barrier during drying, the raspberry skin was subjected to laser pretreatment so as to perforate the surface with pre-selected number of fine holes generated by a CO₂ laser. The perforations allow vapor generated within the bulk of the berry to escape with no resistance of the waxy skin. In addition to studying the effect of perforation parameters on drying time; therefore, quality indicators of the dried product (shrinkage ratio, hardness, rehydration capacity, color, flavor, and anthocyanin content) were also explored. The micropore parameters in experiments were set as follows: P-0 (no perforations), P-3 (12 perforations), P-6 (24 perforations), and P-9 (36 perforations). As expected, greater the number of perforations per berry shorter is the drying time, by up to 23.08%. Moreover, the shortened drying time has a positive effect on product quality as well. The shrinkage rate could be reduced by about 3.95% and the retention rate of anthocyanin could be increased by 20.02%.

Keywords:

• PSMFD
• freeze drying (FD)
• raspberries
• laser perforation
• quality
• energy saving

Acknowledgments

We acknowledge financial supports from the National Key R&D Program of China (Contract No. 2017YFD0400901), Special funds for Taishan Industry Leading Talents Project, as well as Jiangsu Province Key Laboratory Project of Advanced Food Manufacturing Equipment and Technology (No. FMZ202003), all of which have enabled us to carry out this study.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.

Additional information

Funding

This work was supported by the National Key R&D Program of China (Contract No. 2017YFD0400901), Taishan Industry Leading Talents Project, and Jiangsu Province Key Laboratory Project of Advanced Food Manufacturing Equipment and Technology (No. FMZ202003).

Notes on contributors

Ping Qu

Ping Qu is master student in School of Food Science and Technology of Jiangnan University. Her research area is food processing and preservation and she published two papers in international journals.

Min Zhang

Min Zhang is Professor in School of Food Science and Technology of Jiangnan University. His research area is food processing and preservation and he published more than 600 papers in international journals.

Arun S. Mujumdar

Arun S. Mujumdar is Adjunct Professor in Department of Bioresource Engineering, McGill University. His research area is drying technology and he published more than 700 papers in international journals.

Dongxing Yu

Dongxing Yue is senior engineer of Shanghao Biotech Co. in China. His R&D area is food drying technology.