A new study reveals discrepancies in the quality of blueberries in retail markets

A study published in the Foods Journal finds that certain pre-harvest and post-harvest factors can influence the quality of blueberries. However, the phenolic content and antioxidant properties of blueberries, the phenolic content and antioxidant properties of blueberries remain within the expected range at the time of purchase.

Study: Are the blueberries we buy good quality? Comparative study of berries purchased from different outlets. Image Credit: BukhtaYurii/Shutterstock.com

Background

Blueberries are enriched with many phytochemicals, including phenolic compounds. This fruit is considered a «superfood» as its bioactive compounds have many health benefits, including antioxidant, anti-inflammatory, and vasoprotective effects. These nutritional and health benefits make blueberries a very picky fruit globally.

Blueberries are the second most popular berry in the United States after strawberries. Approximately 52% induction in blueberry production has been observed over the past five years.

Fruit softening is caused by various factors, including fungal growth, and can significantly reduce the nutritional quality of blueberries. This is a key aspect to consider when marketing blueberries. However, there is not enough information about the quality of blueberries in retail markets.

In this study, scientists evaluated various quality parameters (texture, flavonoid content, and fungal contamination) of blueberries harvested from ten different retail markets on the same day.

Study design

Blueberries picked from ten markets were randomly divided into three sets as organic replicas. Each set included 136 assembled blueberries. Approximately 40 and 36 blueberries from each set were evaluated for quality and mechanical properties, respectively.

In addition, the total phenolic and anthocyanin content, antioxidant activity, and fungal growth of harvested blueberries were evaluated in the study.

Blueberries produced in cultivation by selective breeding (cultivars) were analyzed separately to identify and quantify phenolic compounds.

Quality assessment

A high sugar content and high acidity are essential for good tasting blueberries. Cranberries with a soluble solids content and titratable acid ratio (SSC/TA) of 10 – 33 and a pH of 2.2 – 4.2 are considered good commercial quality. The SSC/TA ratio is an indicator of the fruit maturity index.

The calculation of the SSC/TA ratio indicated that blueberries harvested from ten different markets have an overall low maturity index.

Mechanical properties

The ripeness stages of blueberries can be differentiated according to their mechanical properties. This study used a penetration test to calculate various mechanical properties, including maximum skin rupture force, displacement at skin rupture, slope at skin rupture, and skin rupture work. Additionally, the equatorial diameter of each blueberry was determined.

The results revealed that blueberries with the highest maturity index had the lowest values ​​of mechanical properties tested. It has previously been observed that the reduced mechanical property of a fruit is an indicator of the ripening process.

However, the scientists could not draw any conclusions based on the evaluation of the mechanical properties because the blueberries analyzed in this study had different ripeness indices, with half below the recommended quality requirements.

Fungal growth

Initial analysis of the blueberries showed no visible signs of fungal contamination. Further sequencing analyzes identified five fungal species in the samples tested. However, there were variations in species-specific contaminations among the samples tested.

Total phenolic and anthocyanin content

The total phenolic content of the blueberries tested ranged from 61.9 to 177.9 mg gallic acid equivalents per 100 g fresh weight, which was lower than previously reported. In this context, evidence indicates that the total phenolic content of fruits can decrease during post-harvest storage.

The total anthocyanin content of blueberries tested ranged from 25.6 to 56.6 mg of cyanidin-3-glucoside per 100 g fresh weight.

Previous evidence indicates that total anthocyanin content shows high variation between blueberry cultivars and that the main reasons for these variations are genotypes and environmental growing conditions.

Antioxidant activity

The antioxidant activity of blueberries was measured by ABTS and FRAP methods. The ABTS method exhibited a wide variation in activity ranging from 16.65 to 40.96 µmol Trolox equivalents/gm wet weight.

Results derived from the FRAP method ranged from 13.22 to 27.38 µmol Trolox equivalents/gm wet weight. A significant correlation in antioxidant activity was observed between the two methods.

A significant correlation between antioxidant activity and total phenolic content was also observed, indicating that the antioxidant properties of blueberries depend on their phenolic content.

Identification and quantification of phenolic compounds

Blueberry samples of known cultivars were used to identify and quantify phenolic compounds. Experiments identified various derivatives of anthocyanins, flavanols, flavanols and phenolic acids. Chlorogenic acid was the only non-anthocyanin phenolic compound detected in the blueberries tested.

The arabinoside and pyranoside forms of malvidin, petunidin and delphinidin were quantified for anthocyanins, as the cyanidin content was below the limit of detection. Delphinidin was the most abundant form, followed by malvidin and petunidin.

Overall, the results revealed that blueberry samples from the same cultivar could have varying levels of anthocyanins, which could be due to pre-harvest and post-harvest practices.

This finding indicates that cultivation practices are not the only factor influencing blueberry quality. However, no difference in anthocyanin levels was observed between organically grown and conventionally grown blueberries.

Meaning of the study

The study indicates that blueberries available in different markets are of acceptable quality at the time of sale. However, the fruits mostly have low maturity indices.