Blueberries are packed with numerous phytochemicals, including phenolic compounds, which make them a true “superfood.”
These bioactive compounds offer a wide range of health benefits, such as antioxidants, anti-inflammatory properties, and protection for blood vessels.
Due to these nutritional and health advantages, blueberries are a globally popular fruit.
In the United States, blueberries rank second only to strawberries in terms of popularity among berries. Over the past five years, there has been a remarkable 52% increase in blueberry production.
Maintaining the quality of blueberries is crucial, as factors like fungal growth can cause fruit softening and compromise their nutritional value. Consequently, this aspect must be considered when buying or marketing blueberries. Unfortunately, there is limited information available regarding the quality of blueberries in retail markets.
To address this knowledge gap, a recent study was conducted to assess various quality parameters of blueberries obtained from ten different retail markets on the same day. The blueberries were randomly divided into three sets as biological replicates, with each set consisting of 136 pooled blueberries. Out of these, 40 were evaluated for quality, while 36 underwent mechanical property analysis.
The study also examined the total phenolic and anthocyanin content, antioxidant activity, and fungal growth of the collected blueberries. Additionally, blueberries produced through selective breeding were separately analyzed to identify and quantify phenolic compounds.
For blueberries to taste good, they need to have a high sugar content and acidity. Commercially, blueberries with a soluble solid content and titratable acid (SSC/TA) ratio ranging from 10 to 33 and a pH of 2.2 to 4.2 are considered of good quality. The SSC/TA ratio serves as an indicator of fruit maturity.
Based on the SSC/TA ratio calculation, the overall maturity index of blueberries collected from the ten different markets was found to be low.
Mechanical properties can be used to distinguish between different maturity stages of blueberries. In this study, a penetration test was employed to calculate various mechanical properties, such as maximum skin-breaking force, displacement at skin breaking, slope at skin breaking, skin-breaking work, and equatorial diameter.
The findings demonstrated that blueberries with the highest maturity index exhibited the lowest values for the tested mechanical properties. Previous observations have indicated that reduced mechanical properties in fruit serve as indicators of the ripening process. However, due to the varying maturity indexes of the blueberries analyzed in this study, the scientists were unable to draw conclusive results based on the mechanical property assessment.
During the initial analysis, no visible signs of fungal contamination were observed in the blueberries. However, further sequencing analysis revealed the presence of five fungal species in the tested samples, with variations in species-specific contaminations between the samples.
The total phenolic content of the tested blueberries ranged from 61.9 to 177.9 mg of gallic acid equivalents per 100 g of fresh weight, which was lower than previously reported. It is worth noting that the total phenolic content of fruits may decrease during post-harvest storage.
Regarding anthocyanin content, the tested blueberries ranged from 25.6 to 56.6 mg of cyanidin-3-glucoside per 100 g of fresh weight. Previous evidence suggests that variations in total anthocyanin content can be attributed to different blueberry cultivars and environmental growing conditions.
The antioxidant activity of blueberries was measured using the ABTS and FRAP methods. The ABTS method demonstrated a wide range of activity, spanning from 16.65 to 40.96 µmol Trolox equivalents/gm of fresh weight. Meanwhile, the FRAP method-derived results ranged from 13.22 to 27.38 µmol Trolox equivalents/gm of fresh weight. A significant correlation in antioxidant activity was observed between the two methods, indicating a dependency on the phenolic content of blueberries.
In terms of phenolic compounds, blueberry samples of known cultivars were analyzed, resulting in the identification of various derivatives of anthocyanins, flavanols, flavanols, and phenolic acids. Among these compounds, chlorogenic acid was the only non-anthocyanin phenolic compound detected in the tested blueberries.
For anthocyanins, the quantification focused on arabinoside and pyranoside forms of malvidin, petunidin, and delphinidin, as cyanidin content fell below the detection limit. Delphinidin was the most abundant form, followed by malvidin and petunidin.
Overall, the study revealed that blueberry samples from the same cultivar could possess varying levels of anthocyanins, which may be attributed to preharvest and postharvest practices. This finding suggests that factors other than cultivation practices influence blueberry quality. However, no significant difference in anthocyanin levels was observed between organically grown and conventionally grown blueberries.
In conclusion, the study indicates that blueberries available in different marketplaces generally meet acceptable quality standards at the time of sale. However, it should be noted that most of these fruits exhibit low maturity indexes.
Image Credit: Shutterstock