Tamarillo: Potential High Value Nutrition Ingredient for Functional Foods With Yoghurt as an Example
Tamarillo is a fruit that contains diverse nutrients, antioxidants and anthocyanins; bioactive compounds with potential for well-being, though research about development of tamarillo-derived foods or exploration of the potential of tamarillo as a functional ingredient is scarce. Three tamarillo cultivars grown in New Zealand (NZ) include the ‘Amber’, ‘Laird’s Large’ and ‘Mulligan’ varieties. Tamarillo pulp and skin were freeze-dried and powdered to increase shelf-life and deactivate enzymes allow testing. This project, therefore, aimed to explore the physicochemical characteristics and potential for health benefits of the New Zealand grown tamarillo (Part I) and to formulate and test the properties, bioactivities and digestibility of yoghurts fortified with tamarillo powder and cubosome-encapsulated tamarillo powder (Part II). From literature, the nutritional adequacy scores of tamarillo has been calculated as 7.9 and 7.4 for gold and red varieties, respectively. The pulp of three NZ tamarillo cultivars all contained ~3% dietary fibre which is higher than other fruits (peach, banana, mango, orange, grape and pineapple) as well as high contents of γ-aminobutyric acid (GABA) which are relatively similar to tomato, one of the greatest sources of GABA. Compared with standard serves of common New Zealand fruits, tamarillos had high α-tocopherol (16-23% AI/serve) and ascorbic acid (67-75% RDI/serve) as well as the highest β-carotene (9-20% RDI/serve). Tamarillos were rich sources of phenolics including anthocyanins and possessed high antioxidant activity. Chlorogenic acid was the most dominant phenolic compound in both peel and pulp of three cultivars, while the main anthocyanin in pulp was delphinidin 3-rutinoside. Tamarillo pulp showed higher total anthocyanins compared to the pulp of strawberry, grape and cranberry fruits. Antioxidant activity of tamarillo exhibited relatively higher values than apples, oranges, red grapes, kiwi fruit, pineapple and were strongly correlated with high total phenolic content. A total of 121 volatiles were found in peel and pulp of three cultivars and principal component analysis clearly showed obvious separation among volatile profiles of different cultivars and tissues of tamarillo. Fifteen volatile compounds had relative odour activity values greater than 1 which means that it could be detected by the human nose, and the key contributor to the overall smell of tamarillo was methional being characterized by tomato-like flavour notes. This could help explain the original name of tree tomato. The results from Part I showed that tamarillo fruit has the potential to be a functional food or a functional ingredient for reformulation of foods such as yoghurt. In part II, yoghurts fortified with tamarillo powder made from pulp were produced either pre- or post-fermentation process. Evidence was produced that tamarillo yoghurt offers the potential for the development of a high-value nutrition product that could be a good dietary source of vitamin C and a source of vitamin E and β-carotene and maintained the volatiles that give tamarillo its distinctive odour and flavour. Addition of tamarillo powder both before and after fermentation increased the acidity, fibre, protein and lactic acid contents of yoghurts. Pre-fermentation produced higher consistency and α-tocopherol concentrations of yoghurt than post-fermentation. Higher elastic modulus, polyunsaturated fatty acids, pro-vitamin A content and retention of vitamin C were observed for post-fermentation samples than pre-fermentation samples. High nutrient contents in terms of essential amino acids, GABA and phenols were observed in yoghurts fortified with tamarillo powder. Addition of tamarillo powder led to a dose-dependent increase in free amino acid content, especially GABA as well as the total essential amino acids of yoghurts in which the pre-fermentation samples showed higher amount of total free amino acids and total essential free amino acids than the post-fermentation ones. The antioxidant capacity of fortified yoghurts from both fermentation processes increased under the influence of in vitro intestinal digestion, probably due to chemical changes of the polyphenols and presence of bioactive amino acids or peptides. Tamarillo bioactives could be effectively encapsulated by cubosome nanoparticles with encapsulation efficiency for most polyphenols was over 50%. Compared to the unencapsulated extract, cubosomal encapsulation provided a protective effect on the tamarillo phenols under simulated gastrointestinal conditions, exhibiting good and sustained release characteristics. The encapsulated tamarillo phenols were almost completely released in alkaline pH conditions (intestinal phase). It was observed that stability of phenols in yoghurt samples showed great potentials after in vitro digestion regarding total phenolics and antioxidant capacity. In addition, each individual bioactive compound of yoghurts in cubosomal system showed the good stability after in vitro digestion. Cubosomes can, therefore, be considered for use to increase the bioavailability of the unique constituents of tamarillo and for use in functional yoghurts. Outcomes in the present study could also have implications for industry to produce value-added yoghurts which are as an important source of dietary bioaccessible phenols. Further work is required to assess the acceptability of these yoghurts to the consumer, the cost of production and viability of sales of the product, shelf life as well as the interaction between fibres and stater culture (viability, total colony counts). Also, interaction between yoghurt components (mainly protein), starter culture and encapsulated bioactives should be evaluated in the future.