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Defining, predicting and delivering ‘fresh’ in the context of leafy salads

Jasper, J. L. (2022) Defining, predicting and delivering ‘fresh’ in the context of leafy salads. PhD thesis, University of Reading

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To link to this item DOI: 10.48683/1926.00103423


Fresh is a general term used to encapsulate the qualities of a leafy salad product, but the term does not have any well-defined meaning that can be empirically measured. Currently, the information provided to the consumer about the condition of a leafy salad product is provided by either a "best-before" or "use-by" date, dependent on if the product is sold as ready-to-eat or not. The current dating system evolved from a stock management system developed in the 1980’s when supermarkets and their increasing volume of products necessitated the inclusion of sell-by dates on packaging to aid store workers. From sell-by dates, "best-before" and "use-by" were developed to inform the consumer about the condition of the product. However, using set chronological dates for indicating biological change is inherently inaccurate and requires a wide margin of error to ensure that consumer safety is not compromised. One issue with having a wide margin of error is that there is a larger potential for waste from the consumer where a product is discarded that may have still been acceptable to consume. Due to climate change, a growing global population and a general under-consumption of fruits and vegetables, there has been renewed interest in the value of on-pack dates. This thesis presented data that focused on the variation of shelf life caused by crop growth environment and storage conditions. To understand better how the visual and physiological properties of leafy salads change over time and how the changes can be predicted, three areas of the agri-food system were investigated. Firstly, the preharvest factors of temperature and cultivar were varied for rocket leaves, and then the impact of the different growth factors on the key nutritional phytochemicals were analysed over a typical shelf life period. Secondly, a more in-depth analysis of the postharvest changes that occur in commercial rocket and lettuce were evaluated as well as the development of non-destructive methods for the postharvest monitoring of leafy salad crops. Variables measured for potential postharvest indicators included aerobic colony count, ammonia, chlorophyll, nitrates, visual quality (by imaging and visual assessment), glucosinolates and glucosinolate hydrolysis products. Finally, the consumer’s attitude towards leafy salads was evaluated in order to be able to relate potential biological markers with consumer rejection. The results show that, as with all biological organisms, growth, development and degredation of leafy salads crops is highly variable as there are many different factors by which they are influenced. In order to provide more accurate, up-to-date information to the consumer about the status of any given product, a dynamic non-destructive method of analysing a product is required. Of all the variables analysed in this thesis, tissue ammonia concentration is the most consistent potential indicator of postharvest status for iceberg lettuce. Furthermore, detectors capable of dynamically monitoring ammonia concentration are able to be incorporated into flexible packaging have been used for high-value products such as red meat but are yet to be tried for leafy salads. For rocket salads, there was no single variable that was consistent in its variation of the postharvest period as to be a useful indicator on its own. However, when considering the initial concentrations of soluble sugars, ammonia and nitrate, the combination may be useful in assessing the postharvest potential of the crop. Implementing this analysis at the point of intake to the packhouse would enable on-pack dates to be flexed in accordance with crop quality and thereby to reduce food waste. It was found that consumers were quite variable in how they view leafy salads, but it was found that age and experience were important when trying to understand the reasons as to why consumers discard products. Older adults tended to rely less on on-pack dates and more on their visual perception of a product when deciding whether to consume the product. Ultimately, to reduce food waste from the consumer, large-scale data acquisition would be required along with dynamic monitoring to develop real time post-retail indicators on pack that would inform the consumer of the quality and safety of the product within.

Item Type:Thesis (PhD)
Thesis Supervisor:Wagstaff, C.
Thesis/Report Department:School of Chemistry, Food and Pharmacy
Identification Number/DOI:
Divisions:Life Sciences > School of Chemistry, Food and Pharmacy > Department of Food and Nutritional Sciences
ID Code:103423
Date on Title Page:2021


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