Developing vacuum-impregnated dehydrofrozen red raspberries with improved mechanical properties

Abstract

The incorporation of red raspberries in bakery and dairy products is limited due to the fragility of the berries. This compromises the appearance of the food product due to the bleeding of juice caused by tissue rupture. In this study, we developed vacuum-impregnated dehydrofrozen red raspberries from fresh fruit. Initially, we optimized drying and freezing conditions for red raspberries that were not vacuum impregnated using air drying alone and in combination with osmotic dehydration, followed by air blasting and cryogenic freezing methods. Later, optimal conditions of partial drying and freezing were used for raspberries that were vacuum impregnated with low methoxyl pectin (LMP) at 10 g of pectin kg⁻¹ of solution and calcium chloride (CaCl₂ · 2H₂O) at 30 g of calcium kg⁻¹ of pectin. Conditions for the vacuum impregnation of raspberries were based on our previous research. The berries were partially dehydrated using hot air (65 °C) until a final water content of 0.65 g of water g⁻¹ of fruit was reached. Next, the berries were placed in glass jars, sealed, and cooled at 4 °C for 2 h. They were then frozen by air blasting and stored for 2 months at −35 °C prior to evaluation. The mechanical properties of the berries, including the maximum force (F_M) and gradient (G_C), were considered to be suitable indicators of fruit firmness. Results demonstrate that raspberries impregnated with pectin and calcium and then partially dried and frozen have higher F_M and G_C values than commercially frozen-thawed berries. These dehydrofrozen raspberries show improved structural integrity for use in bakery and dairy products.

Keywords:

• Air-blast freezing
• air drying
• calcium
• cryogenic freezing
• low methoxyl pectin
• osmotic dehydration

Acknowledgements

We thank Frank Younce, Elizabeth Siler, Prashant Pokhrel, Jungang Wang, Kanishka Bhunia, Todd Coffey and Lisa DeVetter for their technical support and guidance, and Joanna M. Dreger for her assistance. The first author gratefully acknowledges the support and generosity of CONACYT, without which this study could not have been completed.

Disclosure statement

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

Additional information

Funding

This research was funded in part by the Washington State Department of Agriculture Specialty Crop Block Grant Program.