Improving the safety of home-dried foods through modification of treatments and educational programs

Abstract

Microbial illnesses associated with consumption of dried foods raised concerns about the effectiveness of home drying methods for microbial pathogen destruction. Studies at Colorado State University showed that traditional drying methods may allow pathogen survival, and simple modifications enhanced inactivation of Escherichia coli O157:H7, Salmonella and Listeria monocytogenes during home-type dehydration and storage of meat and fruit samples. Cooperative Extension Services personnel recommend blanching or immersion in a salt solution before drying, or oven heating after drying, to help maintain the quality of home dried vegetables. However, treatments have not been evaluated for their ability to minimize potential pathogen contamination. Guidelines for the preparation of safe and palatable dried foods must be developed, made available to, and adopted by home food preservers to help reduce the risk of foodborne illness potentially associated with such products. The objectives of the studies were: 1) evaluate Salmonella survival on inoculated carrot and potato slices prepared using commonly recommended and modified treatments before drying (60°C, 6 h) to determine their influence on inactivation of the pathogen during dehydration and 30 d of storage; 2) evaluate consumer responses to microbiologically acceptable samples of dehydrated fruits (apple, banana, cantaloupe, peach, pear, tomato) and vegetables (carrot, potato) prepared using treatments shown to enhance inactivation of pathogens; 3) develop and evaluate a comprehensive food drying bulletin containing acceptable (safety, appearance, taste) drying guidelines for meats, fruits and vegetables that minimized survival of pathogens; and, 4) develop, conduct and evaluate train-the-trainer workshops designed to encourage adoption of recommended guidelines by home food preservers. Inoculated (Salmonella, 7.8 log CFU/g) carrot slices were subjected to commonly recommended treatments, dried (60°C, 6 h) and stored for up to 30 d. Treatments included: 1) control, 2) steam blanching (88°C, 3 min), 3) water blanching (88°C, 3 min), 4) immersion in 3.23% NaCl (25 ± 3°C, 5 min), and 5) oven heating (80°C, 15 min) after drying. Samples were analyzed by spread-plating on tryptic soy agar with 0.1 % pyruvate (TSAP) and xylose lysine deoxycholate (XLD) agar for bacterial enumeration. After treatment (control samples were left untreated) and 6 h of dehydration, populations were reduced by 1.3-2.0 (control), 4.0-4.7 (steam blanched), 3.5-4.3 (water blanched) and 1.9- 2.6 (3.23% NaCl) log CFU/g. Reductions on samples heated post-drying were 1.7-2.4 log CFU/g. All samples had populations > 1. 7 log CFU/g after 6 h of dehydration and 30 d of storage. It was concluded that modified treatments must be evaluated for their ability to further inhibit pathogen survival during dehydration and storage of carrot slices. Inoculated (Salmonella, 7.8 log CFU/g) carrot slices were subjected to the following treatments: 1) untreated control, 2) steam blanching (88°C, 10 min), 3) water blanching (88°C, 4 min), 4) blanching in a 0.105% citric acid solution (88°C, 4 min), or 5) blanching in a 0.21 % citric acid solution (88°C, 4 min), dried for 6 h at 60°C (140°F), and stored for up to 30 d. Bacterial populations were reduced by 3.8-4.1, 4.6-5.1 and 4.2- 4.6 log CFU/g immediately following steam, water, or citric acid blanching, respectively. After treatment (control samples were left untreated) and 6 h of dehydration, total reductions were 1.6-1.7 (control), 4.0-5.0 (steam blanched), 4.1-4.6 (water blanched) and 4.9-5.4 (blanched in citric acid solution) log CFU/g. Populations were detectable by direct plating at 30 d of storage on all samples except those blanched in 0.21 % citric acid. This suggests that blanching carrot slices, particularly blanching in 0.21 % citric acid should enhance inactivation of potential Salmonella contamination during home-type dehydration and storage. Methods and treatments described above were used to assess the survival of Salmonella during dehydration (60°C, 6 h) and storage (30 d) of potato slices. Initial bacterial populations (6.3-6.6 log CFU/g) were reduced by 4.5-4.8 and >5.4 log CFU/g immediately following steam and water blanching, respectively. After treatment (control samples were left untreated) and dehydration (60°C, 6 h), total Salmonella reductions on blanched potato slices (5.3-5.6 log CFU/g) were significantly (P<0.05) greater than those on control samples (1.9-2.7 log CFU/g). After 30 d of storage, populations were below the detection limit on all samples except for controls. Blanching treatments used in this study enhanced inactivation of Salmonella inoculated onto potato slices and, therefore, may enhance the safety of home dried potato slices if contaminated. Consumers (n = 280) evaluated the sensory characteristics of dehydrated fruits prepared using treatments shown to enhance pathogen destruction. Apple, banana, cantaloupe, peach, pear and tomato samples were left untreated or immersed (10 min, 25°C) in 3.4% ascorbic acid or 1.7% citric acid before dehydration at 60°C. Consumers were primarily female students between the ages of 21 to 34 years. Results showed that acid treatments maintained or improved the appearance and overall acceptability of dehydrated fruit pieces. A booklet (Drying Foods) and a train-the-trainer workshop were developed and pilot-tested with Master Food Preservers, Cooperative Extension agents and consumers (n=75) to encourage adoption of new food drying guidelines. Social Cognitive Theory and the Health Belief Model were used to guide development of the materials and the workshop. Surveys were used to assess food drying knowledge, attitudes and behavior pre- (immediately before), post (immediately following) and 6 weeks following the workshop. Sensory assessments of dried carrot and potato slices left untreated or blanched in 0.105% or 0.21 % citric acid before drying enhanced experiential learning. Knowledge and attitude scores regarding safe food drying methods significantly (P<0.05) improved pre- to 6-week follow up evaluation. Participants also indicated improvements in food drying practices 6 weeks prior to attending the workshop. Outcomes indicate improved subject knowledge, attitude and behavior, which may reinforce adoption of new food drying guidelines.