Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt Effect of drying air temperature and slice thickness on the physical and microbiological quality of dried beef Eunice A. Mewa a,* , Michael W. Okoth a , Catherine N. Kunyanga a , Musa N. Rugiri b a Department of Food Science, Nutrition and Technology, University of Nairobi, P.O. Box 29053-00625, Nairobi, Kenya b Department of Agricultural Engineering and Technology, Egerton University, P.O. Box 536-20115, Egerton, Kenya ARTICLE INFO Keywords: Dried beef quality Physical properties Microbial quality Temperature Beef thickness ABSTRACT The aim of this study was to investigate the influence of cabinet drying air temperature (30–60 °C) and sample thickness (2.5–10 mm) on the quality attributes of dried beef. The physical (colour, rehydration ratio/RR and texture) and microbial quality of beef samples were evaluated using standard procedures. There was a significant decrease (P ≤ 0.05) in L*, a*, b*and chroma/C* colour values with increasing temperature and beef thickness, while change in thickness had no effect (P > 0.05) on the hue/H* colour attribute. The RR was higher at 60 °C for 5–10 mm thick samples and decreased (P ≤ 0.05) with increase in beef thickness. The firmness values in- creased with increase in temperature from 30 to 50 °C, decreased at 60 °C and were significantly lower (P ≤ 0.05) at 2.5 mm beef thickness. The total viable counts (TVC) and Staphylococcus aureus numbers in beef dried at 30 and 40 °C were higher than that of fresh beef, whereas drying at 60 °C significantly (P ≤ 0.05) reduced the microbial numbers. 1. Introduction Meat is the edible part of the skeletal muscle of an animal that was healthy before slaughter (CFDAR, 1990, p. 64). It is preferred as protein source by most people throughout the world due to its distinct flavor and rich nutrient matrix. However, meat is highly perishable, and the lack of proper preservation techniques in the tropics has led to post- slaughter losses; excess meat gets wasted and cannot be stored for use in times of shortage. Sun drying has been practiced for many years and has been used by nomads and pastoralists to preserve meat during excess supply (FAO, 1995). However, it is no longer recommended due to lack of a steady heat source thus difficulty in controlling the drying process. It could also be very time-consuming, with a high risk of contamination from animals, insects, dust, and bacteria (Park, Lee, & Jeong, 2002). Convective hot-air dryers are commonly employed for the industrial processing of various agricultural products in most developing coun- tries. These drying systems reduce food spoilage by sufficiently redu- cing water activity of products, thus inhibiting microbial growth. However, hot-air drying may result in changes to the physico-chemical quality of meat (FAO, 1995) with temperature being the most influ- encing factor. Most changes in meat during drying result from protein denaturation. Especially, denaturation of heme proteins and oxidation of myoglobin pigments which cause darkening of products (Haard, 1992). Protein denaturation also leads to decreased water holding capacity and shrunken muscle fibers, creating a harder and more compact tissue texture (Harris & Shorthose, 1988). These changes in physical structure as well as the chemical properties of meat, as a result determine its ability to rehydrate, or return to its original weight when immersed in water (Farkas & Singh, 1991). Muscles of healthy animals are regarded as sterile, but the slaugh- tering and butchering process creates an opportunity for bacteria to colonize meat surfaces (Olaoye, 2011). The initial microbial load on surfaces of meat to be dried is determined by the hygiene of the abattoir and the handling practices of the meat during butchery and preparation of strips for drying (Mothershaw, Rahman, Mohammed, & Guizani, 2003). Subsequently, the presence of microorganisms in the product determines both its shelf-life and safety. The pathogens of interest in fresh and frozen meat and meat products are; Salmonella spp., Staphy- lococcus aureus, Listeria monocytogenes, Escherichia coli, Yersinia en- terocolitica, Campylobacter spp. and Clostridium perfringens (Mor-Mur & Yuste, 2010). With an increasing demand for high quality dried products that retain their natural characteristics (Fernandes, Rodrigues, Law, & Mujumdar, 2011) and consumer expectation for minimally processed, convenient and safe food products, solar drying is gaining a lot of in- terest. However, in order to optimize the drying process in tropical solar drying conditions, information on dried beef quality in conditions close to that of the real process is needed. The process of beef dehydration https://doi.org/10.1016/j.lwt.2018.02.068 Received 18 August 2017; Received in revised form 4 January 2018; Accepted 27 February 2018 * Corresponding author. E-mail address: eunicemewa@yahoo.com (E.A. Mewa). LWT - Food Science and Technology 92 (2018) 484–489 Available online 03 March 2018 0023-6438/ © 2018 Elsevier Ltd. All rights reserved. T