Linking farm to fruit: Elucidating relations between the growing conditions and intrinsic characteristics of bananas

The banana is one of the most consumed fruits. With the high content of energy and rich nutrition given the minerals and vitamins, the import and export trade of bananas has continued to grow. However, the integrity of the banana supply chain is under threat from food fraud such as mislabelling and falsified organic claims. Food fraud keeps consumers far away from getting the quality assurance they pay for. For bananas, the quality of bananas is often influenced by geographical features such as farm altitude, sunshine duration, rainfall and management systems such as conventional and organic production. Higher-quality bananas also tend to be vulnerable targets for fraudsters, such as organic-certificated bananas. Therefore, this research aims to elucidate the correlation between the banana compositions and growing conditions, in further to provide thorough comprehension to ensure the integrity of the banana supply chain. This thesis addressed a research question of whether the growing conditions and banana quality are highly correlated. In chapter 2, banana pulp and peel samples were collected from 15 Costa Rican farms, and the effects of growing conditions on their stable isotopic ratios and elements were studied in farm-level scope. The soil types impacted the δ13C and δ15N values, however, the δ18O values were influenced more by rainfall and temperature. Due to the effects of volcanic activity on the andic property of soil, the banana samples could be separated into two subgroups according to elemental compositions. Similarly, the stable isotopic ratios and elemental compositions in country-level scope studied in chapter 3 further addressed the critical roles of altitude, monthly mean temperature, annual rainfall and production systems. the higher δ15N values were reported in organic farms, which revealed the effects of organic production systems. The analysis of variance (ANOVA) results showed significant differences in the elemental compositions for most pulp and peel samples. Principal component analysis (PCA) plots showed most farms could be separated according to stable isotopic ratios and elemental compositions of banana pulp and peel at the country level. The related correlation analysis indicated the main distribution differences in geographical origin could be caused by temperature, rainfall and altitude in terms of compositional signatures such as δ13C, δ15N, Mn, Ni, Fe, etc. The combined application of stable isotopes and elements could be used to explore the effects of growing conditions on banana compositions. Further, the volatile and non-volatile compounds of bananas were also analysed in chapter 4. By using the volatile headspace solid-phase micro-extraction gas chromatography (HS-SPME-GC-MS) and real-time high-resolution mass spectrometry (DART-HRMS), the characteristics of different bananas in different geographical origins and production systems were investigated. The geographical origin had a big impact on volatile profiles, however, production systems had a greater impact on non-volatile compounds than volatile compounds. The PCA results indicated that the proportions of some typical volatiles such as 3-methyl-butanol, 2-butyl-2-octenal, and butanol are influenced by local geographical features. Besides, the non-volatile compounds such as zeaxanthin, folic acid, and L-tryptophan were the main contributors to the separation of production systems.  In Chapter 5, the spectral features of banana samples were obtained using hyperspectral imaging (HSI) technology. The PCA plots based on full wavelength could reveal the separated geographical origins and production systems, especially indicted the differences in rainfall, altitude and temperature. To explore the underlying mechanism for the differences in the spectrograms, the content of main chemical compositions such as starch, fibre, carotene, protein and colour values (L*, a*, b*) of banana pulp and peel samples were also detected. Some selected wavelengths such as 405-525 nm, 615-645 nm, and 885-985 nm were found highly related to the contents of carotene, starch, and colour a* and b* values. Regarding, the differences in banana composition coming from the different growing conditions in sampling sites, the portable HSI can provide a first, on-site check of the identity of geographical origins and production systems of bananas. Overall, the novel compositional analysis and spectral imaging combined with data science could be used to explore the banana compositional differences in different growing conditions. Rainfall, altitude, temperature, and organic production systems played important roles to influence the banana quality. It was suggested to further study more geographical features and management details to build robust models for predicting banana origins. The results of this study could contribute to food fraud mitigation in fruit supply chains.