Aspergillus niger inactivation in microwave rotary drum drying of whole garlic bulbs and effect on quality of dried garlic powder

Abstract

Microwave rotary drum drying of whole garlic bulbs was investigated for the Aspergillus niger inactivation and moisture removal. The Weibull and Bigelow models were applied to microbial inactivation data. Garlic bulbs with initial moisture content in the range 1.95–2.14 g water g⁻¹dry matter were dried up to 0.06 g water g⁻¹dry matter. The microwave power density (PD) was varied from 1.03 to 2.67 Wg⁻¹ at 1.5 and 2.0 pulsation ratios (PRs). Effect of PD and PR on A. niger inactivation, product temperature, moisture diffusivity, moisture ratio, drying rate, color, and sensory parameters was studied. Page model was found to be a better fit for microwave rotary drying characteristics of whole garlic bulbs. Microwave rotary drum drying resulted in the average log reduction of A. niger between 1.12 and 1.60. Weibull model predicted A. niger inactivation better than the Bigelow model as it considered the nonlinearity associated with a microbial population in the sterilization process. Garlic powder prepared at 2.0 PR and 1.85 Wg⁻¹ PD was chosen as the best process based on sensory score. The cracking and peeling of garlic cloves were observed during microwave rotary drum drying. The SEM images confirmed the increase in the pore size of the microwave treated garlic sample than the untreated garlic which might be the reason for cracking and loosening of peel in garlic.

Keywords:

• Microwave rotary drying
• pulsation ratio
• power density
• sensory analysis
• Weibull modeling

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors are thankful to the Ministry of Human Resource Development (MHRD) and Ministry of Food Processing Industries (MOFPI), Government of India for their financial support for this research work.

Notes on contributors

Parag P. Sutar

Ms. S. Kar is currently working as a research scholar in the Department of Food Process Engineering, National Institute of Technology Rourkela, India. Dr. A.S. Mujumdar is a renounced researcher in the field of drying and currently working as Adjunct Professor in the Department of Bioresource Engineering, McGill University, Canada. Dr. P. P. Sutar is working as Assistant Professor in the Department of Food Process Engineering, National Institute of Technology Rourkela, India.