Development Prospects of Processing and Utilization of Longtan Pearl Plum

Zhanwen HUANG Mingjuan LI Xiangrong YOU Yayuan ZHANG Ping WEI Ying WANG Kui ZHOU

Abstract Longtan pearl plum， as a new dominant fruit industry in Guangxi， has developed rapidly in recent years and become one of the major economic sources of fruit growers in Guangxi. It has a positive effect on promoting economic development and helping farmers to get out of poverty in Guangxi. But there is almost nothing to do with the processing and utilization. Taking the route of processing and utilization is an inevitable trend of development of Longtan pearl plum industry with the increase of the planting area and yield year by year. In this paper， based on the analysis of edible value of Longtan pearl plum， the development direction of processing and utilization of Longtan pearl plum was expounded， and some suggestions on the problems existing in the processing and utilization were put forward to provide reference for the processing and utilization of Longtan pearl plum.

Key words Longtan pearl plum; Processing and utilization; Development prospects; Problems; Suggestions

Longtan pearl plum is a new variety of famous， special and excellent plum fruits cultivated in Guangxi[1]. After years of cultivation， this variety has the characteristics of selfsufficiency， high yield and late maturity and has the advantages of bright color， crisp taste， unique flavor and rich nutrition， so it is praised as "the first plum of Guangxi" and "the queen of the genus Prunus"[2-3]. Besides， Longtan pearl plum has won the honorary titles of "a highquality agricultural product of Guangxi" and "consumers favorite regional public brand of Chinese agricultural products"， and has been certified as "a nonpollution agricultural product" and an agricultural product with a geographical indication by the Ministry of Agriculture of China[4]. Longtan pearl plum can be as fresh food and be processed， and it is a new characteristic fruit with great development prospects[5].

At present， it has been reported that Cerasus humilis[6-17]， Sanhua plum[18-22]， Angano plum[23-24]， crisp plum[25-26]， Prunus americana[27]， rose plum[28]， Prunus salicina Lindl[29]， Furong plum[30]and other plum varieties can be used to process fruit juice， fruit wine， fruit vinegar， preserved fruit， dried fruit and fruit cake， while the research on Longtan pearl plum is limited to cultivation management， biological characteristics and determination of some nutrients， but there are few reports on the processing and utilization of Longtan pearl plum. In this paper， from the aspects of edible value， development direction of processing and utilization， problems and suggestions of development of processing industry of Longtan pearl plum， the development potential and direction of processing and utilization of Longtan pearl plum will be analyzed to provide theoretical reference for full development and utilization of characteristic Longtan pearl plum resources.

Edible Value of Longtan Pearl Plum

Nutritional value

The average fruit weight of Longtan pearl plum is 21.0 g， and the fruit shape index is 0.8-0.9， so the uniformity is high; the peel is dark purple， and the coloring area is >90%， while the fruit powder is thick[3]; the flesh is yellowishorange yellow， tender， crisp， sweet， and rich in vitamin C， sugar and serine， glycine， proline， glutamine and other amino acids; the fruit has a moisture content of 84%， a soluble solid content of 13.3%， a total sugar content of 93 g/kg， a titratable acid content of 7.3 g/kg， a Vc content of 41.7 mg/kg， and an edible rate of 97.8%; the fruit is sweet and sour and rich in nutrients[31].

Health care function

Longtan pearl plum can promote the secretion of gastric acid and gastric digestive enzymes， promote gastrointestinal motility， improve appetite and promote digestion， and it is more effective especially for a person suffering from gastric acid deficiency， postprandial fullness and constipation. The fruit is rich in minerals such as potassium， calcium， magnesium and zinc， and the physique of the elderly， children and pregnant women can be  enhanced after they eat it. It contains many kinds of vitamins required by the human body， and has high anthocyanin content and effects of antioxidation， antiaging and improving blood vessel elasticity and joint toughness. In addition， Longtan pearl plum also has the effects of diuretic swelling and prevention of liver cirrhosis.

Development Directions of Processing and Utilization of Longtan Pearl Plum

Processing and utilization of fruit juice

Fruit juice is good in color， aroma， taste and nutrition， and can quench the thirst， relieve summer heat and replenish moisture， so it has always been in an irreplaceable position in beverage industry. C. humilis[6-8]， Sanhua plum[18-19]， Angano plum[23]， P. americana[27]， rose plum[28]juice， including clear juice， freshly squeezed juice， original juice and concentrated juice， have been reported. For instance， Chen et al.[6]studied the processing technology of C. humilis clear juice and concluded that after it was blanched for 3 min， decomposed with 0.15% pectase at 55 for 1 h and then clarified with casein， its juice yield， total color and light transmittance were high. Xue et al.[32]found that when C. humilis fruit was processed with 20 mg/L pectinase at 30 for 24 h， the clarity of C. humilis juice was high. Liu et al.[19]studied the processing conditions of concentrated Sanhua plum juice， and found that after 0.005  Zn2+， 0.15% citric acid and 0.015% ascorbic acid were added to Sanhua plum to juice it， the fruit juice was degraded with pectinase at 50 for 1 h， and the extraction rate of anthocyanin in the fruit juice could be improved. After it was concentrated in vacuum at 75 for 1 h， the concentration of anthocyanins could be enhanced more than 10 times. Lei[27]found that after P. americana juice was degraded with 0.03% pectinase at 55 for 2 h， the clarification effect of the juice was the best.

It can be seen that different varieties of plum fruit have great differences in pretreatment， dosage of pectinase， time， temperature， etc. Due to the high content of phenolic substances in plum， if pretreatment is improper， product stability will be affected， and fruit juice is easily discolored or precipitated during storage. With the improvement of peoples quality of life and changes in dietary concepts， the market demand for fruit juice is getting higher and higher， and consumers are more inclined to lowsugar， lowsalt and lowcalorie juice products with both nutrition and healthcare functions. Therefore， for the development of Longtan pearl plum juice， a variety of antioxidants should be used to protect its color and inhibit its browning during processing， and it is necessary to study color protection， enzymolysis， clarification， blending， sterilization and other technological processes according to the characteristics of the variety， overcome key technical problems， and develop natural， nutritious and healthy Longtan pearl plum juice that meet the needs of consumers.

Processing and utilization of fruit wine

Fruit wine has a unique flavor， a mellow taste， low alcohol content and health care function， which is highly sought by consumers. The production process of C. humilis[9-13]and crisp plum[25-26]wine has been studied. For example， Hu Yunfeng et al.[10]degraded C. humilis fruit with 0.02% ICV yeast and 0.1% pectinase at 30 for 1 h to make C. humilis wine. Zhou et al.[13]studied the preparation technology of C. humilis wine as follows： at first， initial sugar content in the liquid of fermentation was adjusted to 18 mg/L， and the inoculation amount of yeast was adjusted to 0.6%; secondly， fermentation was conducted for 7 d under the conditions of temperature 25 and initial pH 3.5; thirdly， 3% sugar， 0.2% lemon acid and 0.05% tartaric acid were added to the wine respectively; at last， 0.08% chitosan was used to clarify the wine. Ren Chunguang et al.[25]studied the  optimum fermentation conditions of complex fruit wine of Rosa roxburghii tratt and crisp plum as follows： the ratio volume of R. roxburghii tratt juice to crisp plum juice was 3≥1; the temperature of primary fermentation was 24， and the temperature of continuous fermentation was 18; the inoculation amount of yeast was 0.4%; sugar content was 25%.

Plum is rich in nutrients， and the original nutrients in the fruit and the nutrients produced in fermentation enter fruit wine， which is beneficial to human health. However， plum contains a lot of pectin and tannin， which affects the juice yield and the taste and stability of the product， and it is prone to discoloration， turbidity and sedimentation during storage[33]. Therefore， freeze concentration， immobilized yeast， alcoholfree fruit wine production， distillation soaking， and other new techniques of fruit wine brewing[34]， as well as enzymatic hydrolysis method， acid reduction method， and gelatin + bentonite combined gluing technology can be used to improve clarity， reduce acidity and acerbity and achieve the purpose of soft taste[9]. Longtan pearl plum is rich in nutrients， bright in color and unique in flavor. It is rich in sugar and vitamins and is a suitable raw material for brewing fruit wine. The development of healthy fruit wine with bright color， rich fruit flavor， mellow taste and high nutritional value will have a good application prospect.

Processing and utilization of fruit vinegar

Fruit vinegar is rich in active ingredients and has very little calories. It has functions such as appetizing and digestion， promoting metabolism， regulating acidbase balance， lowering "three highs" （referring to hyperlipidemia， hypertension and hyperglycemia）， and delaying aging. Fruit vinegar has a certain effect on dispelling the effects of alcohol and liver protection， antisepsis and antiinflammation， prevention and treatment of colds， beauty and weight loss and prevention of "three highs"[35-36]. It can be used in cooking and drinks and can also be used as health food. At present， C. humilis[14-15]and Angeleno plum vinegar[24]have been studied. For instance， Li et al.[14]studied the liquid fermentation process of C. humilis vinegar from the aspects of raw material screening， alcohol and acetic acid fermentation process， and concluded the optimal process as follows： initial ethanol concentration was 6%; the inoculation dosage of acetic acid bacteria was 10%; fermentation temperature was 30; the rotating speed of a shaking table was 120 r/min; fermentation time was 6 d. Pan et al.[15]used 20% C. humilis vinegar and 30% C. humilis juice， 20% fructose syrup and 5% honey to obtain a golden clear fruit vinegar drink with a good taste. Liu[24]proposed that after the enzymolysis of Angeleno plum， orange red， clear and transparent highquality fruit vinegar could be prepared under the conditions as follows： the inoculation dosage of AS1.41 acetic acid bacteria was 5%; alcohol content was 8%; fermentation temperature 32; sterilization was conducted at 95 for 30 s.

In recent years， fruit vinegar has developed rapidly in developed countries such as Europe， America and Japan. However， due to its single product variety and poor quality， small industry scale， lack of leading brands， unclear active ingredients， imperfect industry standards， restricted sales channels and other reasons， the development of fruit vinegar industry have been seriously restricted. Therefore， in the process of developing Longtan pearl plum vinegar， it is necessary to pay more attention to the study of its function and action mechanism， separate and identify functional factors， adopt clarifying agent and membrane filtration combined clarification process， and surmount key technologies that affect quality changes during processing[35].

Processing and utilization of preserved fruit

As a classic and characteristic traditional snack food that is popular among the people， preserved fruit has widely entered in ordinary households， and its consumption has increased year by year. So far， there have been reports on the processing of C. humilis[16-17]， Sanhua plum[20]， P. salicina Lindl[29]and Furong plum[30]preserved fruit or preserves. For example， Zhou et al.[16]used 0.4% CaCl2， 0.2% lemon acid and 0.1% NaCl to protect the color of preserved C. humilis fruit， and then conducted utrasonic sugar infiltration with mixed sugar liquid composed of 30% sucrose， 20% maltose and 10% glucose to produce preserved fruit. Feng et al.[17]firstly used ， 0.5% Vc， 0.5% citric acid and 0.8% CaCl2 to conduct the hardening and color protection of C. humilis fruit， heated it in the mixture composed of 40% sugar solution （sucrose≥glucose=5≥1）， 0.5% NaCl， 0.2% citric acid， 0.6% filler （sodium alginate≥guar gum=1≥1） under 30% microwave firepower for 20 min， and soaked it at normal temperature immersion for 12 h to make lowsugar preserved C. humilis fruit. Gao et al.[29]used pure natural propolis to replace chemical preservatives to prepare P. salicina Lindl preserved fruit and found that 0.05%-0.2% propolis had good antibacterial effect， and did not affect the flavor and quality of the product.

At present， the domestic and international markets are dominated by "highsugar" and "sulphurcontaining" preserved fruit. Longterm consumption of the preserved fruit is not conducive to good health. Therefore， lowsugar and sulfurfree preserved fruit will become the mainstream of consumption. However， the current processing of lowsugar preserved fruit aims mainly to reduce the content of white granulated sugar， so that it has problems such as poor fullness， color and transparency， hard taste and short shelf life[37]. Therefore， innovating the formula， process and technology to develop full， bright， nutritious and healthy lowsugar preserved fruit of Longtan pearl plum with an unique flavor and a pure taste will have great research and development space and market potential.

Processing and utilization of dried fruit

Drying fruit is also one of processing directions of fruit. Although it is not as good as making juice， wine and vinegar in research scope and scale， it is good for fruit storage and can be used as a semifinished product for further deep processing. Fruits and vegetables can be dried by natural drying method， oasthouse drying method， solar drying method， vacuum freeze drying method， microwave drying method and infrared radiation drying method[38]. Lai Chengqing et al.[39]dried plum fruit by the following processes： selecting fruit∪Yaoqing∪washing fruit∪spreading fruit in the sun to dry∪pickling∪spreading fruit in the sun to dry∪secondary pickling∪spreading fruit in the sun to dry∪storage. Longtan pearl plum is sweet and sour， nutritious and unique in flavor. The dried fruit can be processed into preserved fruit， preserves， fruit tea and fruit powder to produce semifinished products.

Processing and utilization of fruit cake

Fruit cake refers to a cakelike product made from fresh fruit that is beaten or juiced， concentrated and dried， to which sweetener， sour agent， gelling agent， etc. are added. It has a rich fruity flavor and an unique taste and retains the original nutrients and color of fruit， so it is very popular among consumers. At present， there are reports on the processing technology of Sanhua plum cake， including sweetener compounding and sterilization[21-22]. The fruit cake made from Longtan pearl plum is not only attractive in color and rich in nutrients， but also meet the needs of consumers for the diversification of processed products.

Problems in the Processing and Utilization of Longtan Pearl Plum

Low level of postharvest commercialization

In recent years， the planting area and yield of Longtan pearl plum in Guangxi have developed rapidly. However， the posharvest commercialization is low， and the capacity is weak. The service system is not perfect. Almost all fruits are still in a backward state of sales. The harvested fruits are not graded and packaged simply or even not packaged. Moreover， cold chain storage facilities and transportation equipment are imperfect， and cold chain circulation can not be achieved. As a result， a large number of fresh fruits appear on the market， so the supply period is short， and the sales pressure is high[40]. Therefore， the postharvest damage is serious， so that the price of firstclass fruit is not high， resulting in certain economic losses.

Blank processing and low economic efficiency

In developed countries， most plum fruits are processed except a small part of fresh plum fruits are sold. For example， in the United States， 45% of plum fruits are processed into concentrated plum juice， and 36% of them are dried， while 3%， 1% and about 1% of them are processed into cans， jam and infant foods respectively[24]. China is the worlds largest producer of plum， and its yield accounts for 48% of the worlds total production. However， the processing industry is backward， and about 90% of fresh plum fruits are eaten， while very few parts of the fruits are are simply processed. At present， the processing of Longtan pearl plum is almost blank. So far， there are no processed products. The resource advantages of the variety have not been fully exerted. The added value of the products is low， almost all of fresh fruits are sold. Due to improper storage and preservation after harvest， fresh fruits rot and are damaged frequently， so the economic benefit is low.

Lack of processing enterprises and backward processing technology

In China， the processing industry of plum fruits starts late and develops slowly. So far， there are no large leading brand enterprises. Some existing processing enterprises have small production scale， simple equipment， relatively backward technology， management concepts and management methods， and lack processed products and brands with independent intellectual property rights. At present， the processing technology and equipment of Longtan pearl plum in Guangxi is almost blank， and no related enterprises have researched and developed the processing technology， equipment， formula and products of Longtan pearl plum.

Insufficient investment in scientific research of processing and utilization

The local government of Guangxi has gradually recognized the value and development potential of Longtan pearl plum， has advocated largescale cultivation. The advantages of resources， price and production conditions are obvious， but the investment in funds， manpower and scientific research of its processing and utilization is seriously insufficient. The technological innovation of processing， project research and development support and cultivation of processing enterprises of Longtan pearl plum are insufficient. Although Guangxi scientific research units have started the research and development of related products， they start late， lack invested human and material resources， lack professional and technical personnel and professional research and development platforms. Research environment is weak， and the research is still at a low level.

Suggestions of Processing and Utilization of Longtan Pearl Plum

Strengthening postharvest commercialization

In the main production area of Longtan pearl plum， it is necessary to build freezers with appropriate scale according to actual production situation， support and encourage professional cooperatives and enterprises to build freezers and refrigerated transportation facilities and equipment， improve the cold chain logistics system of Guangxi， and establish a complete cold chain sales system from the field to the trading market. At the same time， it is needed to research and develop the technical regulations for the harvesting and postharvest commercialization of Longtan pearl plum fruits， and stipulate postharvest processing technology of fresh fruits from the aspects of fruit harvesting， postharvest cleaning， grading， packaging， labeling， storage and transportation， introduce new technologies and new equipment of commercialization handling， achieve the integration of fruit grading， packaging， storage， transportation and processing， and enhance the commodity value of fresh fruits.

Strengthening research on processing and utilization technology， product research and development， and construction of research teams

Based on research on the processing technology of plum， as well as the principles of modern food processing technology and nutrition， the products of Longtan pearl plum should be researched and developed to maximize its economic benefit and expand consumer market. It is necessary to make full use of the existing key research laboratories for processing technology of fruit and vegetable， engineering technology research and development centers and other related research and development platforms， conduct special research on Longtan pearl plum， invest advanced experimental conditions， set up research projects， unite government， scientific research institutions， universities and colleges， and enterprises to tackle various problems， adopt various forms of cooperation such as "enterprise + base + farmer + scientific research" and "cooperative + base + research institutions"， and combine the actual demand of Longtan pearl plum industry to conduct research on major issues and key technology. Meanwhile， a group of professional innovative talent engaged in Longtan pearl plum research should be cultivated.

Strengthening the cultivation of leading processing enterprises and product brands

Most of fruit processing enterprises in Guangxi have problems such as small scale of production， simple equipment and backward technology. It is necessary to combine the existing fruit processing leading enterprises to conduct the promotion， research and development of Longtan pearl plum products， continuously expand the scale of enterprises， introduce advanced equipment and strengthen upgrading and reconstruction of technology， develop and strengthen a number of leading enterprises in processing of Longtan pearl plum， and realize a new pattern of integration of agriculture， industry and trade and onestop development of production， addition and sales. Enterprises should thoroughly understand the consumer demand of the product market， develop new products that meet the market demand， formulate professional brand marketing plans by implementing brand strategy， cultivate independent brands， broaden market channels， and improve market competition force and influence.

Increasing policy support

The government should increase policy support and financial support， research and formulate preferential policies for enterprise processing， encourage processing enterprises to carry out technological transformation and upgrading， design related products and industrial development pilot projects， increase scientific and technological investment in research institutes and universities， and guide more research institutes， universities and enterprises to participate in the development of Longtan pearl plum processing industry. Besides， the government should provide comprehensive guidance on cultivation management， processing technology introduction， sales channels， etc.， lead farmers， cooperatives and enterprises to establish multilevel， multiform and diversified industrial input mechanisms， improve production and management capability and planting enthusiasm， and guide and ensure the healthy development of crop and processing industries through media publicity and promotion of government functional departments. At the same time， it is necessary to increase product market supervision， ensure product quality， and ensure the rapid development of processing industry.

Conclusions

In summary， Longtan pearl plum， as an emerging characteristic advantage resource in Guangxi， has broad development space and prospects. At present， most of fresh plum fruits are eaten directly， and the output is gradually increasing as the planting scale is expanding. If it is still limited to sales of fresh fruits， there will be an inevitable trend of oversupply， poor sales channels and slow sales in the peak season， and industrial development must be restricted. Processing the plum fruits can not only solve the problems of concentrated marketing and being not resistant to storage and transportation of fresh fruits to adapt to the development requirements of food industry， and but also satisfy consumers demand for food diversity. Therefore， it is necessary to develop products such as fruit juice， fruit wine， fruit vinegar， preserved fruit， dried fruit and fruit cake， vigorously develop the processing industry of Longtan pearl plum， and transform variety advantage into market competitive advantage， which has farreaching significance for improving the production， processing and utilization level of Longtan pearl plum and promoting the increase of fruit farmers income.

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