Blueberry (Vaccinium spp.), also known as Yueju or Lanjiangguo in Chinese, are listed as one of the five major health foods for humans by the Food and Agriculture Organization of the United Nations due to their rich content of anthocyanins, vitamin C, ellagic acid and other substances that have both nutritional and health functions (Zhang, 2013). Blueberry is a wild plant native to North America and widely grown around the world. The cultivation of blueberries requires sufficient sunlight and water, and the suitable temperature for growth is between 15℃ and 20℃. The picking period of blueberries is generally from mid June to early July, and they need to be kept refrigerated after harvesting to keep their freshness and nutritional value.

At present, the blueberry industry has become the second largest berry industry in the world after the strawberry industry. With the development of the global blueberry industry, a diversified development trend is gradually forming, and South America, Europe, and East Asia are continuously narrowing the gap with the planting giant North America. There are many types of blueberries, and in recent years, through the efforts of agricultural science and technology workers, we have now bred out species and excellent varieties suitable for cultivation in different climatic conditions such as cold, temperate, and subtropical zones. The cultivation has been promoted in many regions and achieved good economic value.

In recent years, the domestic blueberry market has rapidly expanded, and it is expected to reach $40 billion by 2025 with production exceeding 400 000 tons and become the largest blueberry production and sales market worldwide. However, the domestic market is still dominated by fresh blueberry consumption, and the proportion of frozen blueberries is very low. Now, the largest region for blueberry production and consumption is North America, where both production and consumption of frozen blueberries predominate (http://www. cninfo360. com/y jbg/sphy/qt/20190325/939989. html).

This review comprehensively explores the development status of blueberries as a valuable fruit in terms of production and processing, including the development process of the main production areas of blueberries, the current international trade status of blueberries and the value of blueberry derivative products, in addition to their value as fruit, by integrating data analysis.

1 Analysis of the Nutritional Value of Blueberries

1.1 Blueberry fruit analysis

The blueberry fruit presents a deep blue color mainly composed of anthocyanins, with a sweet and sour taste, sticky pectin, and a special fruity aroma. The fruit contains up to about 13% sugar, which is mainly fructose and glucose; After fruit ripening, the organic acid content is around 1%, among which was mainly citric acid. The average Vc content of fresh fruit is around 10 mg/100 g, with a higher content of vitamin Bg and abundant trace organic substances that maintain normal physiological functions of the human body, such as vitamin A and vitamin E; Blueberries also contain nutrients necessary for the human body to maintain a healthy physiological state, such as macro elements such as Ca and P, and trace elements such as Zn, Fe, Ge, and Gu. It is intuitive from statistics that the content of anthocyanins in blueberries is astonishing (Table 1).

Blueberry fruit is also rich in functional components such as anthocyanins and phenolic compounds, which can alleviate eye fatigue, improve human immunity, protect the health of cardiovascular and cerebrovascular systems, and have a preventive effect on chronic diseases and cancer.

The content of plant fiber in blueberry fruit is extremely high, up to 4.5 g/100 g in general cultivars. The content of anthocyanin pigment in wild varieties is up to 0.33~3.38 g/100 g, while that in cultivars is much lower, generally 0.07~0.15 g/100 g. There are five types of anthocyanins in blueberry fruit: anthocyanin, anthocyanin, primrose, petunia, and methyl flower.

In addition, blueberries are also rich in trace elements, with high levels of iron, potassium, and manganese in their fruit. The blueberry peel also contains polyphenol oxides, chlorogenic acid and other active ingredients. The wild varieties also contain yellow quercetin and flavonol glycosides that are absent from the cultivars. The main source of blueberry aroma is the presence of agarwood oxide, agarwood alcohol, geraniol, and clove oil in blueberries.

Blueberries contain 14% carbohydrates, 0.7% protein, 0.3% fat, and 84% water. Therefore, a 100 g serving provides a relatively low calorie value of 57 kcal with a glycemic load of 6. From this, it can be seen that blueberries are fruit of great health care value (Bu and Zhou, 2010).

1.2 Ultrahigh natural anthocyanins in blueberries

Scientists have found in their research that blueberry fruit contains a large amount of anthocyanins (Meng et al., 2010). The anthocyanins in blueberries are composed of 16 kinds of flavonoids, which have an antioxidant effect about 15 times higher than vitamin E and 200 times higher than vitamin C. Studies have shown that the anthocyanins in blueberries have a 100% bioavailability in the human body. At the same time, anthocyanins in blueberries have the best function compared to other plants, thus, have a wider range of applications.

Blueberries are a natural source of pigments for plants. Its fruit is extremely rich in polyphenolic pigments such as anthocyanins, flavonoids (bioflavonoids) and many other physiologically active components. Polyphenolic natural pigments in blueberries are abundant, and currently, there have been a considerable number of food, pharmaceutical, and health products made from blueberry extracts as the main raw materials in the market.

The high level of anthocyanins in blueberries is very effective for maintaining and regulating true myopia and pseudomyopia, and eliminating eye fatigue, while it also alleviates symptoms such as eye fatigue, blurred vision, fear of light, dry eye, and tearful eye, and also has a certain conservation effect for the middle-aged and old-aged adults with vision loss and presbyopia. Blueberries are rich in free radicals and have significant benefits for protein oxidation, lens opacity, and cataracts in the eyes.

1.3 Vitamin A in blueberries

As early as the Ming Dynasty, Li Shizhen included blueberries as a good wood nourishing medicine in Bencao Gangmu (Compendium of Materia Medica), which has been passed down to this day. In 2000, the US Department of Education also listed blueberries as a nutritional supplement for protecting the eyes of primary and secondary school students. Blueberries have a theoretical basis for protecting vision. High levels of vitamin A are important substances for preventing eye diseases. The presence of antioxidants such as anthocyanins and VE can accelerate the conversion of beta carotene to VA, and quickly replenishing the VA consumed during eye fatigue.

1.4 Abundant superoxide dismutase in blueberries

When a normal gene is attacked by free radicals, there are qualitative changes in its structure and traits that make it to lose its normal genetic function, leading to the occurrence of cancer. But the superoxide dismutase in blueberries, like anthocyanins, is the "number one killer" of oxygen free radicals in the human body, which can resist the invasion of cancer cells, prevent the replication and diffusion of cancer cells, and avoid cancer cells produce polylysin and protease to causing impact and damage to proteins.

1.5 Pectin in blueberries

Pectin is a general term for a type of polysaccharide polymer. Its main function is to effectively remove undigested chyme and a variety of other intestinal toxic substances of the fut in humans, and helping to regulate the balance between postprandial blood sugar and gut microbiota. Pectin content in blueberries is abundant, approximately 1~3 times that in apples or bananas in general. The rich pectin in fresh blueberry fruit can effectively reduce cholesterol, prevent atherosclerosis, and promote cardiovascular health.

2 Blueberry Processing Products

Due to factors such as relatively concentrated picking period, mechanical damage, vigorous physiological metabolism after harvest, and susceptibility to mold infection and softening and decay at the fruit stem, blueberry fruit has a shorter preservation and storage period after harvest. After being stored at room temperature for about 5 days, they will rot (Fang and Xue, 2014). The intolerance of storage and transportation seriously affects the commodity value of blueberries and greatly limits the rapid development of the blueberry industry.

Therefore, new products developed with blueberries as raw materials are constantly sprouting, increasing by 101% over the past 10 years on a global scale according to analysis of data from Inmin, with a particularly rapid increase in markets such as the Middle East, Latin America, and Asia. Among them, infant food (700%), snacks (255%), specialty drinks (224%), breakfast cereal (145%), dairy (143%), alcoholic beverages (100%), and sports and energy drinks (127%) have seen particularly strong growth.

At present, the primary processed products of Chinese blueberries mainly include frozen fruit, concentrated juice, raw material jam, pigments, etc. Frozen fruit is divided into IQF (individual quick frozen) and FD (freeze drying) according to processing technology. Deep processed products mainly include fruit wine, juice, jam, pigment products, yogurt, cake, ice cream, and composite products made with juice as ingredients. In addition, it is also processed into canned goods, jam, fruit powder (crystal), candied fruit, frozen fruit, fruit wine, concentrated juice, fruit juice drinks, and deep processed product extracts (Wang et al., 2020). Foreign producers extract anthocyanins from blueberries to make pharmaceuticals, produce food pigments, and process them into health foods or fine chemical products (Lu and Wang, 2010).

2.1 Blueberry berry processing

Blueberry jam is made from blueberries, sugar, water, and pectin. Blueberry jam is a sweet jam made from blueberries as a major raw material. There are a total of 22 types of blueberry jam products. Due to differences in the origin and quality of blueberry raw materials, the price of blueberry jam products also varies greatly. The price of general blueberry jams is around 15 yuan per 500 g, while sales of jams made from blueberries produced in some good quality origins are around 60 yuan per 500 g. To boost the mouthfeel and extend the quality life of blueberry jam, brandy is added to blueberry jam products (Figure 1).

2.2 Processing of blueberry fruit wine beverage

Blueberry juice is a juice beverage that has a blueberry aroma and is rich in blueberry nutrition. During the production process, nanotechnology is used to make wild blueberries into blueberry pulp stock, which maximally guarantees the fruit color, aroma of blueberries themselves and also guarantees dietary fiber from the maximum. Transforming blueberries makes it easier for the otherwise non absorbable variety of nutrients to be absorbed by the human body.

Blueberry wine, usually made from low shrub varieties and natural wild blueberries, is made by fermenting and ripening the flesh and skin of blueberries. When blueberries are fermented into liquor, not only their nutrients are maximally retained, but also their multiple nutritional elements, such as anthocyanins, selenium, amino acids, zinc, and iron, are more abundant and easily absorbed by the human body. According to research, blueberry wine has 50 times the anthocyanin content of apple and 30 times that of grapes, so so it has also been widely used as liquid gold and oral cosmetics (Xin et al., 2010).

2.3 Blueberry jelly and candy food processing

Blueberry candy mainly includes candy products with blueberry flavor, such as soft candy, hard candy, chewing gum, etc. Most blueberry candies are processed from blueberry juice and blueberry essence. In the manufacturing process of blueberry flavored chewing gum, the same pigments as blueberry color and the essence with blueberry flavor are mainly added, so in a strict sense, blueberry flavored chewing gum is actually only a synthetic substance of blueberry flavor, and only a very few have components of natural blueberry juice. Addition of blueberry concentrated juice was also predominant in blueberry flavored jelly products. So people still need a clear understanding of the “blueberry taste” during consumption (Liu and Gu, 2012).

2.4 Blueberry enzyme

Blueberry enzyme is a functional microbial fermentation product produced from the fermentation of blueberries by various beneficial bacteria, containing rich nutrients such as vitamins, enzymes, minerals, and secondary metabolites (Mi, 2016). The main reason why blueberry enzymes have been expanded globally is that the production of enzymes is not limited to blueberry production areas, so production enterprises can be spread all over the world. Non blueberry producing areas such as Fujian and Guangdong in China also have blueberry enzyme production enterprises. Enterprises can also develop different varieties of products, such as high, medium, and low, depending on different raw materials and market demands, and the price of products varies from 50 RMB to several thousand RMB (Figure 2).

3 Production and Development Status of Blueberries in Various Production Regions of the World

It is precisely because of the unique flavor and nutritional and health value of small berries that the blueberry fresh fruit and its derived products take the world by storm. Due to market demand exceeding supply, blueberry products are expensive in the international market. According to statistics, the retail price of fresh fruit in the market is as high as 10~20 USD/kg. The sales price of frozen blueberries in the international market is also around 2 600~4 000 USD/ton. In addition, blueberry derivatives, such as concentrated fruit juices processed from blueberry fruit, sell for up to 30 000~40 000 USD/ton in the international market.

North America, Europe, and Japan are currently the largest consumer and trading markets for blueberry products. Japan is the largest importer of blueberry products in Asia. In 2004, the import volume of fresh blueberry fruit reached 4 000 tons and the import volume of frozen blueberry fruit reached 10 000 tons.

3.1 Production and yield status of blueberries in North America

Although the United States is the leading country for blueberry production, there is no fresh fruit production from September to April of the following year of each year, due to market demand, during which time fresh fruit was mainly imported from Chile, Australia, and New Zealand at 20 000 tons. However, the market's needs still cannot be met. According to statistics, 90% of the blueberries produced in Australia and New Zealand are exported to North America.

Global blueberry production has maintained a stable increase, and fresh fruit remains the main product form of global blueberry production. The global blueberry production in 2020 was 1.388 million tons, with an increase of 8.7% year-on-year from 1.277 million tons in 2019; Among them, the fresh fruit production is 0.962 million tons, accounting for 69% of the total production; The processing volume is 426 000 tons, which is higher than that in 2019.

On a global scale, North America is the birthplace and main production area of blueberries. In the past decade, the cultivation techniques of North American blueberries have also been continuously improved, with the main blueberry varieties cultivated being high-bush blueberries. With the continuous increase in blueberry planting area in various countries around the world, the North American region with the largest increase has increased by about 1.5 times, and the planting area in China has also increased by about 5 times. The continuous increase and expansion of production areas is one of the reasons that cannot be ignored for the rapid increase in blueberry production.

At present, blueberries have become the main fruit tree species. According to statistics, by 2021, the cultivation area in North America has reached 1.1514 million acres, with a total yield of over 497 700 tons. As is well known, blueberries originated in the United States. As early as the early 1990s, blueberries had become the second largest berry fruit tree after strawberries. There are 36 states in the United States and 6 provinces in Canada that produce blueberries. There are 7 states in North America where highbush blueberries are cultivated on more than 450 hectares, followed by Michigan, New Jersey, North Carolina, Oregon, Kansas, Washington, and New York in order; After the United States, various areas of the world are competing for planting and cultivation, and in Canade, the provinces of British Columbia and Nova Scotia covered more than 450 hectares.

3.2 Development status of blueberries in South America

Blueberry cultivation has the characteristics of simple management techniques, long plant lifespan, relatively few diseases and pests, short fruiting period, and high economic benefits. In addition, there are many varieties of blueberries. Through the unremitting efforts of technical workers, excellent varieties suitable for cultivation in different climatic conditions such as cold, temperate, and subtropical regions have been selected and promoted in many regions of the world, most of which have achieved good economic value. So the current situation of blueberry cultivation around the world can be described as blooming everywhere.

The blueberry industry in South America began in Chile. The cultivation techniques of blueberries in Chile are basically introduced from the United States, but in order to better adapt to the local growth in Chile, researchers have improved and innovated based on the original foundation and according to the conditions of the country, thus, forming a set of matching cultivation techniques that can well adapt to the geographical and climatic characteristics of Chile.

Because Chile has a long and narrow geographical distribution from north to south, it has both humid subtropical climate and marine climate in the south, as well as a Mediterranean climate in the central part. Most regions of the country have four seasons, with long lighting hours and large temperature differences between day and night. Due to its unique geographical location, its fruit mostly matures and goes on sale from November to March of the following year. This is the cold winter season in the Northern Hemisphere, therefore the fruit export market has great potential.

With the continuous expansion of blueberry cultivation area in South America, the production has rapidly increased in the past decade. Compared with major regions around the world, the production of blueberries in South America has even surpassed that of its birthplace North America, becoming the world's largest blueberry production area. In 2020, the production of blueberries in South America reached 387 000 tons, accounting for 27.9% of the global total production, with 321 000 tons of fresh fruit produced; The production in North America is 364 000 tons, accounting for 26.3% of the global total production; The Asian region is the region with the fastest growth rate of global blueberry production (Figure 3).

3.3 Development status of blueberries in Australia

In the 1950s, blueberries were first introduced to Australia, but ultimately failed. Until the early 1970s, the Victorian Department of Agriculture imported seeds from the United States and began selection experiments, which continued until the mid-1970s when the Australian Blueberry Growers Association was established. Moreover, in 2017, some growers in Australia stated that the production of fresh grapes had exceeded demand in the past few years, and the increasing saturation of grape fruit sales in the market led to difficulties for fresh grape growers, which led to a large number of growers starting to switch to blueberries to increase their income. Changing the original grape planting to blueberries has further expanded the planting area of blueberries as well.

3.4 Development status of blueberries in Asia

In Asia, Japan is the only country engaged in industrialized production of blueberries. Since 1951, Japan has gradually introduced high-bush blueberry varieties from the United States and started cultivation, but the development speed and results are not optimistic. Until the mid-1980s, the cultivation area in Japan was only 1 hectare. With the increasing emphasis on blueberry production, the cultivation area of blueberries in Japan increased from 200 hectares in 1993 to 530 hectares in 2005, with a blueberry yield of 1 500 tons that year.

The main varieties cultivated in Japan are high-bush blueberries and rabbit eyed blueberries. With the continuous improvement of blueberry cultivation technology in Japan, it has also increased the interest of other Asian countries in blueberry cultivation. Although the planting area of blueberries has rapidly increased in the Asian region, Japanese blueberries are still mainly imported, mainly due to Japan’s expensive labor costs, relatively small planting area, as well as the high cost of fresh fruit harvesting. Howvever, at the same time, Japan’s consumption of blueberries is increasing day by day.

According to statistics, more than 30 countries and regions around the world have started industrialized cultivation of blueberries, with a total area of 2 million acres up to now. However, blueberries are still in short supply in the market (Figure 4).

4 Summary and Comments

Global blueberry cultivation and planting began in the United States. So far, the United States and Canada in North America have ranked among the world’s top in terms of cultivation area, yield, technology research and development, and industrialization level. European countries introduced and cultivated blueberries relatively late, but developed rapidly. The advantage of European countries lies in their abundant wild blueberry resources, which laid the foundation for their development of blueberry processed products. The Asian region began cultivation for blueberry production using Japan as a representative. With the widespread planting of blueberries, technical issues such as blueberry varieties, cultivation, and seedling cultivation that are suitable for local climate and soil conditions are constantly being optimized.

The trend of diversification in the main producing areas of blueberries is evident globally. In recent years, the global blueberry cultivation regions and areas have been continuously increasing, with the number of countries and regions cultivating blueberries increasing from 58 in 2016 to 71 in 2020. The global planting area increased from 132 560 hectares in 2016 to 205 670 hectares in 2020, with an increase of 73 100 hectares and a total growth rate of approximately 55.11%. The proportion of North America, which has long dominated blueberry cultivation, decreased from 58.79% in 2008 to 38.40% in 2016 and 25.56% in 2020. Countries such as Peru and Canada are increasingly expanding their blueberry industry scale (Ma et al., 2014).

However, as an important emerging industry in fruit cultivation, the development prospects of blueberries are still worth exploring at a deeper level all over the world. This is not only because blueberries are known as the world’s third-generation fruit that combines health and nutrition, but also because they are not easy to store and have a relatively short fruiting period, which urgently needs to be solved to meet people’s demand for fresh fruit and growing material life needs. Vigorously developing blueberry production is beneficial for market expansion and economic efficiency improvement, thereby driving the development of the entire fruit industry.

Authors’ Contributions

DDY is the project leader and responsible for literature collection, paper writing, finalization, and translation; YSY and HYP were responsible for editing and proofreading. All authors read and approved the final manuscript.

Acknowledgements

This study was's upported by Funding for Cuixi Innovation Research&Development Project of Cuixi Academy of Biotechnology, Zhuji.

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