Mandarin fruit quality: a review.

During the last decade, there has been a continuous rise in consumption and global marketing of fresh, easy-to-peel mandarins, with current annual production of nearly 29 million tons. Nevertheless, most of the existing knowledge on quality traits of citrus fruit comes from research conducted on oranges and grapefruit, which are the main products for the citrus juice manufacturing industry; relatively little is yet known regarding the unique fruit quality traits of mandarins, nor about the great diversity in these traits among the various natural sub-groups and varieties of mandarins. In the present review we discuss the physiological, biochemical, and molecular factors governing key fruit quality attributes of mandarins, including fruit colour, size and shape, ease of peeling, seedlessness, flavour, and nutritional quality. Fruit colour, size, and shape contribute to external appearance; peelability and seedlessness to ease of consumption; and flavour and nutritional quality to internal quality. © 2017 Society of Chemical Industry.

Diversity among mandarin varieties and natural sub-groups in aroma volatiles compositions.

BACKGROUND: Mandarins constitute a large, diverse and important group within the Citrus family. Here, we analysed the aroma volatiles compositions of 13 mandarin varieties belonging to seven genetically different natural sub-groups that included common mandarin (C. reticulata Blanco), clementine (C. clementina Hort. ex. Tan), satsuma (C. unshiu Marcovitch), Mediterranean mandarin (C. deliciosa Tenore), King mandarin (C. nobilis Loureiro), and mandarin hybrids, such as tangor (C. reticulata × C. sinensis) and tangelo (C. reticulata × C. paradisi). RESULTS: We found that mandarin varieties among tangors ('Temple', 'Ortanique'), tangelos ('Orlando', 'Minneola') and King ('King') had more volatiles, at higher levels, and were richer in sesquiterpene and ester volatiles, than other varieties belonging to the sub-groups common mandarin ('Ora', 'Ponkan'), clementine ('Oroval', 'Caffin'), satsuma ('Okitsu', 'Owari') and Mediterranean mandarin ('Avana', 'Yusuf Efendi'). Hierarchical clustering and principal component analysis accurately differentiated between mandarin varieties and natural sub-groups according to their aroma-volatile profiles. CONCLUSIONS: Although we found wide differences in aroma-volatiles compositions among varieties belonging to different natural sub-groups, we detected only minor differences among varieties within any natural sub-group. These findings suggest that selecting appropriate parents would enable manipulation of aroma-volatile compositions in future mandarin breeding programmes.

Effects of packinghouse operations on the flavor of 'Orri' mandarins.

Mandarins have a delicate flavor and are easy to peel and easy to consume. However, they are relatively perishable and suffer from flavor deterioration after harvest. The goal of the current study was to examine the effects of commercial packinghouse operations on the flavor of 'Orri' mandarins. For that purpose, we collected fruit from four different points along a commercial citrus packing line: (1) directly from the harvest bin, (2) after application of a hot (53°C) fungicide treatment for 30 s, (3) after waxing, and (4) after waxing and after the fruit had passed through a hot-air drying tunnel (37°C) for 2 min. The collected fruit were stored for 3 or 6 weeks at 5°C and then kept for five more days under shelf-life conditions at 22°C. The observed results indicate that the hot fungicide treatment had no effect on flavor quality. However, the waxing and waxing +drying treatments resulted in significant increases in ethanol accumulation, lower flavor-acceptability scores, and increased off-flavors. Gas-chromatography mass-spectrometry (GC-MS) analysis revealed that the waxing and waxing +drying treatments resulted in particular increases in the levels of alcohol and ethyl ester volatiles; whereas levels of other aroma volatiles (i.e., esters, aldehydes, monoterpenes, and sesquiterpenes) decreased after storage in all fruit samples. Overall, the waxing process in commercial citrus packinghouses increased ethanol and ethyl ester volatile levels and harmed flavor acceptability. These findings demonstrate the need to identify new wax formulations that do not hamper fruit-flavor quality.

Biochemical and Molecular Factors Governing Peel-Color Development in 'Ora' and 'Shani' Mandarins.

To identify factors governing peel-color development in mandarins, we examined carotenoid content and composition and the expression of carotenoid-related genes during four stages of ripening (i.e., green, breaker, yellow, and orange) in two varieties: 'Ora', which has orange fruit, and 'Shani', which has orange-reddish fruit. The two varieties had different carotenoid compositions, and 'Shani' had a significantly higher level of total carotenoid pigments. 'Shani' was rich in the deep orange ß-cryptoxanthin and the orange-reddish ß-citraurin, whereas 'Ora' was rich in the orange violaxanthin. RNA-Seq analysis revealed significantly greater expression of the carotenoid-biosynthesis genes PSY, ßLCY, ßCHX, and CCD4b, as well as MEP-pathway genes and several ethylene-biosynthesis and -signaling genes in 'Shani' fruit. In contrast, the expression levels of genes involved in the synthesis of α-branch carotenoids (i.e., εLCY and εCHX) and ZEP, which is involved in the formation of violaxanthin, were significantly higher in the 'Ora' fruit.

Diversity in sensory quality and determining factors influencing mandarin flavor liking.

We evaluated the sensory quality of 42 mandarin varieties that belong to 7 different natural subgroups: common mandarin (Citrus reticulata Blanco), Clementine (Citrus clementina Hort. ex. Tan), Satsuma (Citrus unshiu Marcovitch), Mediterranean mandarin (Citrus deliciosa Tenore), King mandarin (Citrus nobilis Loureiro), and mandarin hybrids, such as tangor (Citrus reticulata × Citrus sinensis) and tangelo (Citrus reticulata × Citrus paradisi). Consumer flavor acceptance tests revealed wide diversity in flavor preferences among mandarin varieties and subgroups. Furthermore, descriptive flavor-analysis tests conducted with the aid of a trained sensory panel revealed that the 9 most preferred varieties had similar flavor profiles, characterized by high sweetness, moderate to low acidity levels, low bitterness and gumminess, strong fruity and mandarin flavor, and high juiciness. The average total soluble solids (TSS) and acidity levels among the highly preferred varieties were 13.1% and 1.1%, respectively. In contrast, the 8 least preferred varieties were either too sour or gummy or had low levels of sweetness, fruity, or mandarin flavor, and either high acidity levels (>1.4%) or low TSS levels (<12.0%). Pearson tests revealed significant positive correlations between flavor acceptance and perceptions of sweetness, fruitiness, and mandarin flavor, and negative correlations with acidity levels and perceptions of sourness, bitterness, and gumminess. Principle component analysis clearly distinguished between highly accepted varieties that were tightly correlated with high TSS levels and perceptions of sweetness fruitiness and mandarin flavor, as compared with the least accepted varieties that were correlated with high acidity levels and perceptions of sourness, bitterness, and gumminess.

Genetic diversity among mandarins in fruit-quality traits.

A detailed phenotypic analysis of fruit-quality traits was conducted among 46 mandarin varieties within the Israeli Citrus breeding collection, belonging to genetically different natural subgroups, including common mandarin (C. reticulata Blanco), clementine (C. clementina Hort. ex. Tan), satsuma (C. unshiu Marcovitch), Mediterranean mandarin (C. deliciosa Tenore), King mandarin (C. nobilis Loureiro), and mandarin hybrids, such as tangor (C. reticulata × C. sinensis) and tangelo (C. reticulata × C. paradisi). Evaluated qualities included physical attributes (size, shape, color, peel thickness, and seed number); physiological properties (ripening period, peelability, and segmentation); nutritional and biochemical composition (vitamin C, phenol, flavonoid, and carotenoid contents and total antioxidant activity); and sensory attributes (total soluble solids and acid levels, flavor preference, sweetness, sourness, and fruitiness). The results indicated wide genetic variability in fruit-quality traits among mandarin varieties and natural subgroups, and statistical and hierarchical clustering analysis revealed multiple correlations among attributes. Such phenomic analysis is an obligatory requirement for identification of molecular markers for distinct fruit-quality traits and for selection of appropriate parents for future breeding programs.

Ripening attributes of new passion fruit line featuring seasonal non-climacteric behavior.

The passion fruit hybrid cultivar 'Passion Dream' (PD) produces two cycles of fruiting per year, in the summer and winter. Self-hybridization of PD created various lines, including 'Ripens during Summer' (RS), which lacks the ability to abscise during winter, suggesting a seasonal nonclimacteric behavior. The two lines were characterized by several quality traits: PD produced high ethylene levels in both seasons; RS produced significantly less ethylene during summer and almost none during winter. The ratio of total soluble solids to titratable acidity (TSS/TA), and aroma volatiles production, as determined by solid-phase microextraction/gas chromatograph-mass spectrometer (SPME/GC-MS) techniques, and taste indices were highest in PD summer fruits and lowest in RS winter fruits. Peel color in PD was affected by environmental and storage temperatures, whereas RS fruits always showed a strong purple color. The present findings suggest that ethylene production levels in passion fruit greatly influence various ripening processes, including acid degradation, increased TSS/TA ratio, accumulation of aroma volatiles, and tastiness.