Introduction

Feijoa (Acca sellowiana), a perennial shrub in the Myrtaceae family with shiny, evergreen leaves and showy white and red flowers, is also known as "goiabeira serrana" in Brazil, "guayobo del pais" in Uruguay, and "guavasteen" or pineapple guava in Hawaii. The autumn-producing fruit is a dark green, aromatic berry that can be smooth or rough, with 4-5 transparent locules, a gritty pericarp, and vascular bundles that soften as the berry ripens.¹ The highlands of southern Brazil, north Argentina, Uruguay, and east Paraguay are where feijoa originated, but it has since spread to other countries for commercial production, albeit as a minor crop: New Zealand, Colombia, California, Georgia, Portugal, Italy, Australia, Brazil, and Azerbaijan.² According to reports, the fruit develops better flavour in warm climates, which increases its chances of being further developed commercially.³ Feijoa is rich in vitamins, minerals, and phytochemicals and has a remarkable flavour and aroma that is preserved through processing. A variety of processed goods are available, such as ice cream, yoghurt, chocolates, pies, wines, jams, liqueurs, and juices. It is known as "sociable fruit" because, despite its short storage life, many home gardeners share their harvest with neighbours and friends to reduce losses. Although feijoa is commercially produced in Brazil, Colombia, Georgia, Italy, and other countries, only New Zealand regularly releases statistics on feijoa production. According to the most recent report by Aitken and Warrington (2020), the nation has approximately 200 feijoa growers who produced 1100 tonnes of fruit from 150 ha worth NZ$ 3.2 M (domestic) and NZ$ 0.1 M (export, free on board (FOB)). These figures show how exporting feijoa can grow considerably. Feijoa is mostly traded in local markets or through pricey, constrained air freight because it is a minor crop with low tonnage and a short storage life (of about 4 weeks when stored at 4°C).⁴

Nutritional profile of feijoa

Based on fresh weight (FW) data, the fruit is considered a good source of sugars (8.2%) and dietary fibre (6.4%). Furthermore, it provides 32.9 mg of vitamin C and 172 mg of potassium per 100 g (FW). Protein (0.6–0.8%, 4 genotypes, FW) and fats (0.3–0.4%, 4 genotypes, FW) are both found in comparatively small amounts in the fruit.  Twelve genotypes of fruit were grown in Italy, and the ascorbic acid content of their fruit flesh varied from 25 to 40 mg/100 g FW (fresh weight), sourced from various countries.⁵ It has been documented that there is genetic diversity in the total phenolic (93–251 mg gallic acid equivalents/100 g FW) and flavonoid (14–33 mg catechin equivalents/100 g FW) contents of fruit flesh across 12 genotypes grown in Italy. Numerous polyphenols have been found in the fruit and peel, leaf, flower bud, and branch of the feijoa plant, among other botanical parts. Additionally, the flesh was found to contain pyrocatechol, eriodictyol, rutin, gallic acid, ellagic acid, eriocitrin, and syringic acid.⁶ Within the intact fruit, the most prevalent volatile compounds were methyl benzoate (39.2%), followed by ethyl butanoate (29.6%), ethyl benzoate (10.6%), trans β-ocimene (4.7%), ethyl hexanoate (1.2%), and heptan-2-one (0.8%). In feijoa, methyl and ethyl benzoates accounted for more than 90% of the volatile oil. Over 96% of the oil content was composed of 67 different compounds. β-Caryophyllene (12%), ledene (9.6%), α-humulene (6.3%), β-elemene (4.9%), and δcadinene (4.8%) were the main constituents in the oil.⁷ It was found that the main volatiles in the leaf were α-copaene (6.6%), aromadendrene (12.5%), β-caryophyllene (27.8%), and limonene (36.2%).⁸ The primary fatty acids found in the seeds were determined to be linoleic acid (84.4%, w/w), oleic acid (7.2%), palmitic acid (5.6%), and stearic acid (2.8%). As such, unsaturated lipids can be obtained from seeds.⁹ Fruit from feijoas is a potassium source. Eleven genotypes of Turkish feijoa fruit and leaf mineral composition showed genetic diversity. For example, iron (Fe) and zinc (Zn) ranged from 38–200 ppm and 2.9–7.3 ppm in fruit, respectively, while Fe and Mn ranged from 63–148 ppm and 18–63 ppm in leaves.¹⁰ Compared to other fruit varieties, feijoa fruit was found to have a comparatively high oxalate content. The fruit flesh of feijoas (1 genotype) had levels of soluble and insoluble oxalate of 18 and 42 mg/100 g (FW), respectively. Kidney stones can result from consuming a diet high in soluble oxalate. To reduce the amount of soluble oxalate consumed, feijoa fruit should only be consumed sparingly and in small amounts.¹¹

Mechanisms of action

It is anticipated that the variety of bioactive compounds found in feijoa will contribute to a host of health benefits. The antioxidant properties of extracts from the fruit and leaf of feijoa have been investigated both in vitro and in vivo. The findings demonstrated the varying degrees of antioxidant and radical scavenging capabilities exhibited by the feijoa fruit and leaf extracts. Compared to the flesh, the fruit peel exhibited a greater level of antioxidant activity. The presence of several bioactive substances, including vitamin C and polyphenols, could be easily linked to the antioxidant activity of the feijoa fruit extracts.¹² Both in vitro and in vivo studies have demonstrated the anti-inflammatory properties of feijoa fruit products. Feijoa fruit extract had in vitro inhibitory activities against adenosine monophosphate kinase (AMPK) and Janus kinase 2 (JAK2) among the extracts of 49 distinct common food items. JAK2 and AMPK kinases have been linked to a number of illnesses, including Crohn's disease associated with inflammation. According to fractionation-guided analysis, ellagitannin played a significant role in the in vitro anti-inflammatory effect. An acetonic fruit extract demonstrated anti-inflammatory properties in an in vitro study; this effect may have been facilitated by the fruit's flavone and stearic acid content. Numerous earlier studies did, in fact, demonstrate the varying degrees of anti-inflammatory properties of various polyphenols. Among other fruit kinds, the specific combination of polyphenols and other bioactive substances in feijoa fruit samples showed strong anti-inflammatory properties.¹³

Flavone was found to be an effective anti-cancer compound in feijoa fruit extract against solid and haematological cancer cells in an in vitro study. Though further research must be done in vivo, specific polyphenols found in feijoa fruit, such as flavone, may be the cause of the fruit samples' reported anti-cancer properties in vitro.¹⁴ In vitro antibacterial and antifungal activities against a variety of microorganisms were demonstrated by the extracts of feijoa fruit and leaves. A significant antimicrobial component found in the extract was found to be flavone. It successfully stopped rhizoctonia solani (a fungus) and helicobacter pylori from growing. The presence of bioactive polyphenol compounds like ellagitannins and sorbic acid in feijoa fruit and leaf extracts may be the cause of their antimicrobial activity.¹⁵ Tyrosinase inhibition, analgesia, nephroprotection, anti-deprecation, sun protection, serving as a probiotic carrier, and enhancing disaccharidase activity are among the additional biological characteristics. Its ability to promote the formation of collagen and skin regeneration, along with its antibacterial, moisturising, anti-inflammatory, and antioxidant properties, make it a crucial component of skin health and hence in skincare products.¹⁶

Methods of consumption

Typically, feijoa is eaten as fresh fruit that has ripened. Scoop out the flesh with a spoon after cutting it in half, just like you would with a kiwifruit. The feijoa's flesh oxidises quickly, turning brown. After the fruit has been peeled, submerge it in either fresh lemon juice or a solution of salt and water. Feijoa that has been canned or jellied is more common in Brazil, though. Juice and alcoholic drinks are also made from it. You can also cook feijoa to make pies, tarts, puddings, fritters, dumplings, pastry fillings, and ice cream flavourings. It can be used to make crystallised fruits, sauces, jellies, chutneys, relishes, and sparkling wines.

The plant's thick petals can be eaten raw or cooked, and they taste spicy. 

Although the flesh of unripe feijoas can be quite firm and the taste less appealing, eating them raw is generally not harmful. Additionally, there may be a lower concentration of healthy nutrients and antioxidants. The higher acidity and lower developed fibre content of unripe fruits may cause discomfort in some individuals' digestive tracts. In order to prevent eating spoiled feijoas, one should be aware of the following symptoms: 

• Mouth Feeling or mushy: an overripeness that becomes spoiled
• Discoloration: Any visible mould growth or strange dark patches 
• Odour: If the fruit has an unpleasant or sour odour, it shouldn't be eaten 
• Taste: Avoid eating fruit if it has an unpleasant or fermented flavour 

The presence of spoilage is an obvious sign that the feijoa is unsafe to eat. It has more to do with appropriate storage and shelf life than it does with how ripe the fruit is.

Conclusion

Feijoa is a fruit that has many uses. In addition to being high in vitamins, minerals, and phytochemicals, it is processed to retain its amazing flavour and aroma. The fruit is regarded as an excellent source of fats, sugars, dietary fibre, potassium, vitamin C, and protein. Feijoa contains a wide range of bioactive compounds that have antioxidant, anti-microbial, anti-inflammatory, and anti-cancer effects, among other health benefits. The fruit doesn't have any severe side effects, but it's still best to use caution when eating it, especially if you have certain medical conditions.