The increasing market demand for fresh produce promotes a keen interest in developing a rapid, sensitive and reliable method for monitoring plant health and determining the shelf-life of postharvest produce. The objective of this study is to explore the capability of Surface-enhanced Raman spectroscopy (SERS) in these applications. SERS integrates Raman spectroscopy which measures molecular vibrations and nanotechnology which enhances the weak Raman signals. Herein, we developed two SERS methods based on a surface detection approach using nanoparticles solution and a headspace detection approach using gold nanoparticles (AuNPs) fibers, to detect biochemical changes during postharvest storage of arugula leaves. Compared with surface detection, the headspace detection revealed significant spectral changes during the storage, particularly in the shifts around 500, 950 and 1030 cm-1. These changes analyzed using principal component analysis (PCA) to establish a prediction model for shelf-life determination. Through analyzing reference standard compounds, we identified the dimethyl disulfide (DMDS), 1-propanethiol and methanethiol (MT) were most likely to account for the signature spectra of headspace arugula at the late storage period due to the activities of spoilage bacteria. The headspace detection method was also applied to monitor the stress responses of living basil to abiotic stresses (pesticide/salinity). However, the volatile analysis of the basil plants response to abiotic stresses (pesticide/salinity) showed indistinctive results. In conclusion, the headspace detection based on SERS provides a new strategy for quality monitoring of fresh produce in the food industry.

Thesis (M.A. Agricultural Management (Agricultural Economics)) -- University of Limpopo -- 2020 / Potato is the most important vegetable crop in South Africa in terms of contribution to the gross value of agricultural production, export earnings and contribution to food supply base and food security in the SACU region. Despite the importance of this commodity, very little is known about the nature of price transmission between different levels of potato value chain in South Africa. The study aims to determine the nature of price transmission in the South African potato market. The objectives of the study are to investigate the existence of long-run equilibrium relationship between producer, wholesale and retail prices; to determine characteristics of the relationship; and to determine the direction of price causality. The study made use of Error Correction Model and Granger Causality test. The Empirical results reveal the existence of price asymmetry in the South African potato value chain. Furthermore, the results show that retail prices are more responsive producer price increases than they are to producer price declines. The Granger causality test shows that prices in potato value chain are determined mainly at the wholesale level (i.e. at the National Fresh Produce Markets). The study recommends further research focusing on price transmission for other basic food commodities and that the government retains and strengthens the existing food price monitoring system. / Department of Agriculture, Forestry and Fisheries

Small islands developing states (SIDS) sustainability is a United Nations’ aim. Their markets are often influenced by external policies imposed by larger economies. Could an anti-competitive measure affect the food vulnerability of a SIDS? This research examines the effects of an external non-tariff measure (NTM) on Puerto Rico’s (PR) agribusinesses. It explores the effects of a maritime cabotage regulation (US Jones Act) on the affordability and accessibility of produce and grains. PR imports 100% of their needs of grain and over 85% of fresh produce. PR’s food imports are generally from the US and the trade service is restricted to the use of the US maritime transportation. As a result, the supply chain of these two sectors although different, are limited by the US Act that may impact the cost of food, its availability, firms’ efficiency and other structures of production. Using a mixed convergent design, PR’s agrifood supply chains were explored and analysed in relation to the maritime cabotage regulation. Oligopolistic structures and collusion between maritime transporters and local agribusinesses importers limit the access to data, but other internal factors also have a role. Fieldwork shows that while the cabotage regulation itself is a constraint, interaction with others NTM and the current political framework between US and PR are relevant. Factors such as lack of efficiency, poor innovation and a self-limitation of the agribusinesses firms were found. The novelty of this research is the use of mixed methods to evaluate the effects of cabotage on the agrifood supply chain.

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Submitted in fulfilment of the requirements for the degree of Master of Applied Science in Food Science and Technology, Durban University of Technology, 2015. / Listeria monocytogenes have been implicated as a public health concern worldwide. The study explored the survival of non-adapted, heat adapted and chlorine adapted L. monocytogenes on tomatoes; as well as the survival of non-adapted, heat adapted and chlorine adapted biofilms after exposure to sodium dodecyl sulphate (SDS), levulinc acid, sodium hypochlorite solution. Contact time of 1, 3 and 5 minutes was used. The survival of L. monocytogenes was monitored at 0, 24, 48 and 72 hours. The sanitizers were used individually or combined as follows; 1% sodium dodecyl sulphate individually; 0.5% levulinic acid individually; 200 ppm sodium hypochlorite solution individually and 0.5% levulinic acid/0.05% sodium dodecyl sulphate in combination (mixture). The samples were kept at 4 °C throughout the period of assessment. The effect of these sanitizers on pH, total soluble solids (TSS) and titratable acidity (TA) was also determined. Furthermore, the attachment of L. monocytogenes on tomatoes was investigated using a scanning electron microscope. Highest log reduction of non-adapted L. monocytogenes were observed on tomatoes treated with 1% SDS and least log reduction was achieved when tomatoes were treated with sodium hypochlorite solution. Though the log reduction achieved by 0.5% levulinic acid was higher that sodium hypochlorite solution, it was lower than log reduction achieved when 0.05% SDS / 0.5% levulinic acid mixture was used for all contact times. Using non-adapted L. monocytogenes, SDS was able to destroy all L. monocytogenes at 1, 3 and 5 minutes contact time. The trend was the same when heat adapted and chlorine adapted L. monocytogenes were used. There was no significant log reduction observed with biofilms. More favourable results were observed as contact time was increased from 1 to 5 minutes. Though there was a decrease in surviving bacteria from 1 to 3 minutes contact time, this decrease was not significant. The study investigated if exposure to sanitizer has an effect on pH, titratable acidity (TA) and total soluble solids (TSS) of the tomatoes. It was revealed that levulinic acid and mixture can have detrimental effect on pH, TA and TSS of tomatoes. The TA and TSS of samples treated with levulinic acid and mixture varied significantly (P ≤ 0.05) compared to the control sample. Although the TA and TSS of samples treated with SDS and sodium hypochlorite solution were different from the control, the differences were not significant. As much as sanitizers have the potential to reduce the bacterial population in fresh produce they may not completely destroy pathogens. Chlorine based sanitizers such as sodium hypochlorite though frequently used in the fresh produce industry, are not the best sanitizer to be used against food borne pathogens. Other sanitizers such as SDS used alone or in combination with another sanitizer can achieve better results than the widely used sodium hypochlorite solution as observed in this study. Stress adapted pathogens become less responsive to sanitizers during subsequent treatments. Through this research, it was established that biofilms are resistant to sanitizers. Though application of sanitizers in fresh produce is cheaper and simpler to apply, there is need to monitor varying concentrations of sanitizers, contact time and minimise contact with sub-surfaces as this could lead to sensory quality losses.

No description available.

<p dir="ltr">The necessity for on-farm, point-of-need (PON) nucleic acid amplification tests (NAATs) arises from the prolonged turnaround times and high costs associated with traditional laboratory equipment. This thesis aims to address these challenges by developing devices and a user-interface application designed for the efficient, accurate, and rapid detection of <i>Bacteroidales</i> as an indicator of fecal contamination on fresh produce farms.</p><p dir="ltr">In pursuit of this, I collaborated with lab members to engineer a Field-Applicable Rapid Microbial Loop-mediated isothermal Amplification Platform, FARM-LAMP. This device is portable (164 x 135 x 193 mm), energy-efficient (operating under 20 W), achieves the target 65°C with ± 0.2°C fluctuations, and is compatible with paper-based biosensors for loop-mediated isothermal amplification (LAMP). Subsequently, I led the fabrication of the microfluidic Field-Applicable Sampling Tool, FAST, designed to deliver high-throughput (10 samples per device), equal flow-splitting of fluids to paper-based biosensors, eliminating the need for a laboratory or extensive training. FARM-LAMP achieved 100% concordance with standard lab-based tests when deployed on a commercial lettuce farm and FAST achieved an average accuracy of 89% in equal flow-splitting and 70% in volume hydration.</p><p dir="ltr">A crucial aspect of device development is ensuring that results are easily interpretable by users. To this end, I developed a Python-based image analysis codebase to quantify sample positivity for fecal contamination, ranging from 0% (no contamination) to nearly 100% (definite contamination) and the concentration of field samples. It utilizes calculus-based mathematics, such as first and second derivative analysis, and incorporates image analysis techniques, including hue, saturation, and value (HSV) binning to a sigmoid function, along with contrast limited adaptive histogram equalization (CLAHE). Additionally, I developed a preliminary graphical user interface in Python that defines a prediction model for the concentration of <i>Bacteroidales</i> based on local weather patterns.</p><p dir="ltr">This thesis encompasses hardware development for on-field quantification and the creation of a preliminary user-interface application to assess fecal contamination risk on fresh produce farms. Integrating these devices with a user-interface application allows for rapid interpretation of results on-farm, aiding in the effective development of strategies to ensure safety in fresh produce operations.</p>