Increasing Knowledge on Postharvest Handling of Goji Berries (Lycium barbarum L.)

Goji berry (Lycium barbarum L.) is a fruit of solanaceous family that is widely found in arid and semi-arid regions of northwestern China, southeastern Europe and the Mediterranean. China represents the biggest producer worldwide representing its 85,000 ha of cultivated field and 98,000 t of fruits produced per year. Goji berries, also known as wolfberries, traditionally utilized in Chinese medicine, have become increasingly popular in the western world because of their nutritional properties. Generally, goji berries are cooked and processed as tea, soups, or served with meat and vegetables. They are also utilized for juice, tincture, and wine production. The fruit is also consumed in dried form or processed in powdered form for medicinal purposes. Given their high perishability, high water content, and susceptibility to damage and rot, fresh goji berries are generally available in areas where they are cultivated. This is also due to the lack of information on goji berry postharvest behavior and storage recommendations. From a pomology point of view, goji berry's first fruition is typically observed in 3- year-old plants. The mature fruit is 1 to 2 cm long, with an ellipsoid shape and a bright orange-red color similar to mature mini-tomato, and contains 20􀂱40 tiny seeds per fruit. It is sweet and has a tangy aroma. It is reported that the green stage is the most appropriate for extracting organic acids for pharmacological purposes. The red stage is processed into dried fruit for direct consumption, benefiting from sugars and L-ascorbic acid content. There is no indication of its use as a fresh fruit. However, there is no clear information regarding the characterization of fruit maturation stages, and the classification in terms of climacteric or non-climacteric fruit has not been explored. Therefore, we identified several maturity indexes from different stages of maturity, including physical properties such as length, width, weight, color (hue), firmness, soluble solid content (SSC), pH, and titratable acidity (TA). Fruit dimensions increased from class 1 to 6 starting from 8.08 mm length, 3.95 mm width, and 0.07 g of weight, to 16.26 mm, 13.15 mm, and 1.29 g, respectively. Soluble 10 solids increased from 2.68 % to 23.5 %. Goji berries showed climacteric behavior indicated by a climacteric peak during the early stages of development. This included changes to TA and SSC, which from class 4 to 6 stabilized around the maximum value of 23 % after eight days of storage at room temperature. Their high nutritional value was confirmed by the content of vitamin C, which is comparable to that of citrus fruit. It reached the maximum value of 0.52 g/kg at full ripening, whereas the phenolic content decreased during ripening to values of 2.15 g/kg. This contributed considerably to the high antioxidant content of the berries. Temperature and relative humidity are the first storage conditions to be accurately controlled to preserve quality and allow maximum shelf-life. Studies on goji berry have only considered low (0 and 2 °C mostly) or high (10 or 20 °C) temperatures. Several studies reported the effect of temperature on postharvest quality of fresh goji berry fruit during storage at different temperatures (-2, 0, 10, and 20 °C) and concluded that 0 °C was the optimum temperature to maintain the berry phytochemical and sensory qualities. However, these results are not reliable because of the large temperature gap among the tested temperatures and did not include refrigeration temperature of 5 °C, which is used in the cold chain of fresh or minimally processed products for transport and sale. As goji berries belong to the Solanaceae family, they are plausibly chilling-sensitive, such as tomato, bell pepper, and eggplant. However, the quality of fruit stored at 0 °C may show a slower degradation compared to that of fruit stored at 10 or 20 °C. Therefore, one experiment was aimed to test the effects of low storage temperatures between 0 and 7 °C to identify the best storage temperature for maintaining goji berry quality and shelf-life, with particular attention to the occurrence of chilling injury symptoms. Fruit stored at 0 °C showed the lowest respiration rate and ethylene production (5.82 mL CO2 kg-1h-1 and 0.667 μL C2H4 kg-1h-1, respectively); however, at this temperature, the highest incidence and severity of shriveling and dark spots was observed reaching 59 and 15.42 ¯ter 12 days of storage. In contrast, 5 °C was found to be the best storage temperature for goji berry fruit; the fruit appeared fresh 11 and healthy and had the highest scores during sensory analysis with a general acceptable impression, with the lowest damage attributable to chilling injury; 27.14 % fruit presenting shriveling; 6.17 % black spot damage. Storage of goji berries at 7 °C resulted in the lowest marketability and the highest incidence of decay due to accelerated senescence processes. Significant differences were also found in the phytochemical attributes, vitamin C content, SSC, TA, SSC/TA ratio, total polyphenol content, DPPH, and anthocyanin content. Another important technology to prolong the shelf-life of fresh fruit is controlled atmosphere (CA) storage. Increasing CO2 concentration respect to air levels, depending on crop tolerance, may results in shelf-life extension due to its fungistatic effect and to the inhibition of ethylene synthesis and action. Fruit were stored in air enriched with 5 %, 10 %, 20 % CO2, and 0 % for the control in air, for 22 days at 5 °C. Goji fruit stored under CO2 concentration of 20 % showed the highest quality allowing a reasonable shelf life up to 20 days. Fruits stored at 5 % and 10 % and in air showed higher susceptibility to decay represented as firmness losses and severity of mold infection. Regarding chemical composition main differences regarded antioxidant activity, which increased for the treatment at 5 % and 10 %. Optical fruit sorting and selection is a very critical step of the handling of fruit. The demand for a rapid, and non-destructive tool for the selection of defective fruit is increasing. Moreover, internal quality and composition is a very valuable information which can also be obtained thanks to the potentiality of new optical methods. Hyperspectral Spectroscopy Imaging (HIS) is one of the tools to obtain information about external and internal quality of fruit, with an added value for small fruit, very sensitive to manual handling and manipulation. HIS was used to discriminate defective from sound fruit. As for common damages, the defects were identified as mild (i.e. visual damage, softening, bruise), moderate (i.e. pitting, initial mold), and severe damages (i.e. severe mold). Hyperspectral imaging (HIS) system in the Vis-NIR ranges was used for the defect detection using visual appearance analysis, as reference measurement. The outcomes of this study indicate the 12 promising potential for visible-NIR to provide non-invasive, rapid, and reliable early detection of common disorders in goji berry fruits. As for the prediction on the internal composition in term of Vitamin C, total antioxidant, phenols, anthocyanin, soluble solids content (SSC), and total acidity (TA), Hyperspectral Imaging (HIS) in the Visible- Near Infrared (VIS-NIR) (400􀂱 1000 nm) and in the Near Infrared (NIR) (900􀂱1700 nm) was applied. For vitamin C and AA, partial least square regression (PLSR) combined with different data pretreatments and wavelength selection resulted in a satisfactory prediction in the NIR region obtaining the R2pred value of 0.91. As for phenols, SSC, and TA, a better performance was obtained in the VIS-NIR region yielding the R2pred values of 0.62, 0.94, and 0.84, respectively.