Infrared Drying Characteristics and Quality Variations of Lily Bulbs Under Blanching Pretreatment

Abstract

Infrared drying characteristics and quality variations (color change, hardness, contents of polyphenol and flavonoid) of lily bulb under blanching pretreatment are investigated. Influences of parameters such as pretreatment temperature and time, and infrared drying temperature are discussed. Effective moisture diffusion coefficient, activation energy and energy consumption were calculated. The drying time was reduced by 62.5%, 56.3% and 61.5% at 90 C compared to 60 C when blanching time was 4, 5 and 6 min, respectively. A blanching time of 5 min and drying temperature of 70 C were ideal for pretreatment and drying to maintain good color quality. Hardness value of lily bulb decreased as drying temperature and blanching time increased. 70 - 80 C was ideal drying condition to maintain good hardness quality. Blanching time and drying temperature differently affected contents of flavonoids and polyphenols of lily bulb. Basically, when blanching time was relatively long and drying temperature was relatively high, the content of flavonoids and polyphenols was high. Traditional lily bulb drying methods, sun drying and fire drying, may cause browning, and hence nutritional value and appearance quality are deteriorated. Infrared drying has high drying efficiency and good preservation of nutrients, and blanching pretreatment can effectively alleviate the degree of browning. Thus infrared drying with blanching pretreatment is ideal for lily bulb drying, however, investigations are limited. This paper presents effects of pretreatment temperature, pretreatment time and infrared drying temperature on drying kinetics and quality variations to provide guidance for storage and processing of lily bulb.

Sea Buckthorn Pretreatment, Drying, and Processing of High-Quality Products: Current Status and Trends

“…Physical pretreatment is mainly divided into thermal and non-thermal treatments. They include microwave, blanching, ultrasonic, steam blasting, and pulsed electric field [67][68][69]. Physical pretreatment methods for sea buckthorn currently include blanching, piercing, ultrasonic waves, etc.…”

Chemical Composition Analysis of Lilium brownii var. Viridulum Baker and the Effect of Postharvest Primary Processing on Its Quality

“…Yuan et al studied the effect of different drying processes on the changes in regaloside A content in fresh bulbs of Lilium [15]. Huang et al studied the infrared drying characteristics and quality changes (color change, hardness, polyphenol, and flavonoid content) of Lilium bulbs before blanching treatment [50]. However, the contents of extracts and polysaccharides in the processing process were not measured according to the provisions of the Chinese Pharmacopoeia.…”

“…This study improved the quality control of the primary processing of Lilium. [50]. However, the contents of extracts and polysaccharides in the processing process were not measured according to the provisions of the Chinese Pharmacopoeia.…”

Effect of Microwave Treatments Combined with Hot-Air Drying on Phytochemical Profiles and Antioxidant Activities in Lily Bulbs (Lilium lancifolium)

“…Significant color changes occur during hot-air drying [ 4 ]. Prolonged exposure to high air temperatures or long processing times can cause some undesirable quality changes in lily-bulb products including browning, oxidation, case hardening, and the degradation of nutrition and natural flavor [ 11 ]. Browning during the processing and storage of lily bulbs involves enzymatic and non-enzymatic browning, the former being mainly due to the oxidation of polyphenols by browning-related enzymes, including polyphenol oxidase (PPO) and peroxidase (POD), while the latter is mainly due to the carbonyl ammonia reaction between lily polysaccharide compounds and amino acids during storage and transport [ 12 ].…”