Postharvest Biology and Technology 59 (2011) 124–131 Contents lists available at ScienceDirect Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio Lettuce quality loss under conditions that favor the wilting phenomenon M.V. Agüero a,b,∗ , A.G. Ponce a,b , M.R. Moreira a,b , S.I. Roura a,b a Grupo de Investigación en Ingeniería en Alimentos, Facultad de Ingeniería, Universidad Nacional de Mar del Plata, Juan B, Justo 4302, 7600 Mar del Plata, Argentina b Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina article info Article history: Received 11 June 2010 Accepted 25 August 2010 Keywords: Greenhouse lettuce Physical indices Greenness index Microbiological indices Nutritional index Wilting abstract While temperature management is a usual accepted practice and is the simplest and easiest way of delay- ing vegetable deterioration, maintenance of the recommended relative humidity (RH) during postharvest storage is not always carried out. The objectives of this work were to simulate two RH conditions: optimal (95–98%) and low (70–72%) during the storage of lettuce heads at recommended temperatures (0–2 ◦ C), and to address how deviation of RH from optimal conditions affects lettuce quality indices. The effects of storage on quality parameters were assayed as follows: weight loss and water content as physical indices, chlorophyll content as a greenness index, native microflora (mesophilic bacteria, psychrotrophic bacte- ria, lactic acid bacteria, total coliforms, yeast and molds) as microbiological quality indices, ascorbic acid retention as a nutritional quality index, and overall quality as a sensory acceptability index. Additionally, these indices (with the exception of weight loss) were analyzed in three lettuce sections: external (com- posed by outer and older leaves), middle (composed by mid leaves) and internal (composed by inner and younger leaves). Shelf-life of lettuce was significantly affected by RH. The exposure of lettuce heads to low RH drastically reduced shelf-life by 75%. Plants exposed to low RH had considerable weight loss from the first day to the end of storage. For both RHs, the middle and internal sections did not show chloro- phyll changes during storage while the external section showed pigment degradation characterized by first order kinetics. Ascorbic acid underwent first order degradation for all situations (sections and RH conditions), but with different degradation rates. The microbial population counts were slightly affected by RH. The overall quality of lettuce stored at low RH decreased rapidly. The shelf-life of material stored at this relative humidity condition was 5 days, when the overall quality scores of middle and external sections were below the acceptability limit and only the internal section had a score above the limit. In addition, overall quality of lettuce stored at optimal RH decreased slowly. At day 5 of storage the three lettuce sections had high scores and the product was satisfactory. Only at day 20 did the external section show a score just on the acceptability limit. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Fresh leafy vegetables have a short shelf-life when they are exposed to unfavorable postharvest conditions. The shelf-life is a rapidly changing dynamic process in which product composition, associate microbial population, temperature, relative humidity, light and package atmosphere changes have high levels of inter- action (Moreira et al., 2003). Certain physical and chemical attributes of leafy vegetables have been used as quality indices. Moisture loss leads to weight loss and shrinkage during storage. Postharvest water loss can cause rapid deterioration reducing quality through shriveling. As well, ∗ Corresponding author at: Grupo de Investigación en Ingeniería en Alimentos, Facultad de Ingeniería, Universidad Nacional de Mar del Plata, Juan B, Justo 4302, 7600 Mar del Plata, Argentina. Tel.: +54 0223 481 6600; fax: +54 0223 481 0046. E-mail address: mvaguero@fi.mdp.edu.ar (M.V. Agüero). green colour retention is an obvious indicator of the leafy veg- etable quality and has a great impact on consumer selection. For green vegetables, chlorophyll content is associated with greenness (Roura et al., 2000). Also fresh vegetables are a major source of ascorbic acid, a nutrient that besides its vitamin action is valuable for its antioxidant effects, its stimulation of the immune sys- tem and other health benefits that are being actively investigated (Giannakourou and Taoukis, 2003). Another basic phenomenon that can compromise shelf-life extension of fresh vegetables is microorganism proliferation. A knowledge of the native microflora of fresh vegetables and its change under different environmental storage conditions is of fundamental importance when this prod- uct is traded as a fresh commodity in which microorganisms play a primary role in keeping quality (Ponce et al., 2002). The quality and shelf-life of lettuce (Lactuca sativa L.) is limited by dehydration. Moisture is lost when vegetables are stored below optimum humidity levels (95–98% relative humidity, RH). Low rel- ative humidity during storage or sale increases the transpiration 0925-5214/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2010.08.018