Original Research ArticlePhysicochemical properties and proximate composition of tamarillo (Solanum betaceum Cav.) fruits from New Zealand
Introduction
Tamarillo, also known as tree tomato (Solanum betaceum Cav.), is relatively low in carbohydrates, though it is a good source of dietary fibre; vitamins A, B6, C and E; minerals including calcium, copper, iron, magnesium, manganese, phosphorus and zinc (Vasco et al., 2009). It possesses a variety of functional bioactives, such as phenolics, anthocyanins (Diep et al., 2020) and carotenoids, that are beneficial to human health (Skinner and Hunter, 2013). New Zealand is one of the main producers and exporters of tamarillo with a yield of approximately 450 tons per annum. The country possesses a cultivated area of some 10 ha with 40 growers (Aitken and Warrington, 2018). Three cultivars, which differentiate by colour and size, are called Mulligan (purple-red), Laird’s Large (red) and Amber (yellow). The red cultivar contributes to approximately 80 % of the total tamarillos exported from New Zealand (Schotsmans et al., 2011).
Consumer acceptance of fruits is influenced by skin colour, firmness, size and weight. The skin of tamarillo is green at development stage and turns into a full yellow, orange or red colour during maturation stage and the firmness decreases (Schotsmans et al., 2011). In the first 25 weeks of development, total soluble solids (TSS) increase to 12°Brix. Breakdown of starch and accumulation of reducing sugars are seen as fruit matures (Ramírez and Kallarackal, 2019). However, starch accumulation is not associated with tamarillo growth nor TSS content in tamarillos, which is different from tomato, the fruit of the same Solanum genus. One of the vital quality and maturity features of fruits is sugar content, where glucose and fructose are the major components (Hu et al., 2016). Soluble sugars start to accumulate from ripening and these serve as substrates for respiratory reactions, which significantly influence the development of overall flavour and texture of tamarillo (Hu et al., 2016). Most of previous studies have focused on reporting on glucose, fructose and sucrose (Acosta-Quezada et al., 2015; Vasco et al., 2009), except for Gannasin et al. (2015) who had detected eight soluble sugars, except fructose, from different fractions of Malaysian tamarillo.
Amino acid content is a result of metabolic changes during growth and ripening of fruits, hence this parameter can be used to identify the optimum ripening time (Silva et al., 2004). Amino acids affect quality of fruits in terms of aroma, colour and taste. When heat treatment is involved in producing fruit-derived products such as juices and jams, amino acids play a greater role in influencing aroma, colour and taste through Maillard reaction (Silva et al., 2004). Evaluation of amino acid in fruits may help to identify falsification or adulteration in fruit-derived products, including wines, juice and jam (Silva et al., 2004). The presence of six essential amino acids (arginine, histidine, isoleucine, phenylalanine, valine, and threonine) had only been reported in Malaysian tamarillo (Gannasin et al., 2015) where tryptophan and lysine were absent and methionine was found in trace amount. Though tamarillo belongs to the same Solanum genus as tomato, which is one of the richest sources of γ-aminobutyric acid (GABA) (Saito et al., 2008), the presence of GABA had never been reported in tamarillo to date. Understanding the relationships between the external measures of fruit quality (skin colour, weight and size) and the chemical compositions (pH, TSS, protein, dietary fibre and carbohydrates) will lead to simple and quantifiable indicators of fruit quality. Much of the available data on composition of tamarillo do not reflect the large diversity of cultivars and they are several decades old (Lister et al., 2005).
In this study, physical properties (fruit weight, size and skin colour) and chemical properties and compositions (pH, TSS, proximate components, reducing sugars and amino acids contents) of Amber, Laird’s Large and Mulligan tamarillo cultivars, differentiated in pulp and peel, were examined. The primary objective of this study was to document the composition of tamarillos sourced from New Zealand with a specific focus on unusual varieties, Amber and Mulligan.
Section snippets
Collection and preparation of tamarillo
Fifty commercially mature, fresh fruits of Amber (yellow), Laird’s Large (red) and Mulligan (rich purple-red) tamarillo cultivars were collected from growers in Whangarei, the Northland region of New Zealand. All three cultivars were collected under the same agricultural conditions. Commercial maturity was between 21 and 24 weeks from anthesis. Thirty fruits were randomly selected and washed to determine physical characteristics (weight, length, diameter and colour), followed by proximate
Physical properties of tamarillo
The three cultivars were significantly different from each other in size, colour and proximate content (Table 1). The Amber and Laird’s Large were twice the weight of the Mulligan (P < 0.05). The mean diameter of the Mulligan was significantly lower by 22.7 % and 26.6 % compared to the Amber and the Laird’s Large, respectively. For the length, Mulligan was significantly shorter, by 17.6 % and 21.1 %, than that of the Amber and the Laird’s Large, respectively. Size and weight are two most
Conclusion
Amber, Laird’s Large and Mulligan cultivars grown in New Zealand were examined in terms of physical properties, proximate compositions and reducing sugar and amino acid profiles. Significant differences (P < 0.05) of these features were found among the cultivars. PCA has further explained the variance observed in reducing sugars and amino acids between cultivars and between tissue types. Tamarillo showed a high content of dietary fibre compared to other commonly consumed fruits. The amino acid
Authorship contributions
Conception and design of study: Tung Diep, Michelle Yoo, Chris Pook; acquisition of data: Tung Diep, Michelle Yoo, Chris Pook; analysis and/or interpretation of data: Tung Diep.
Drafting the manuscript: Tung Diep; revising the manuscript critically for important intellectual content: Tung Diep, Michelle Yoo, Chris Pook.
Approval of the version of the manuscript to be published (the names of all authors must be listed): Tung Diep, Michelle Yoo, Chris Pook.
Declaration of Competing Interest
The authors declare no conflict of interest.
Acknowledgments
The authors would like to acknowledge New Zealand Tamarillo Growers Association for providing tamarillo fruit. The authors would like to thank the Riddet Institute for the Doctoral Scholarship provided to the first author. The authors would like to acknowledge Performance Based Research Fund, provided by School of Science, Faculty of Health and Environmental Sciences, in AUT university.
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