Scientia Agricultura Sinica ›› 2020, Vol. 53 ›› Issue (10): 2078-2090.doi: 10.3864/j.issn.0578-1752.2020.10.014

• SPECIAL FOCUS: QUALITY OF AGRICULTURAL PRODUCTS • Previous Articles     Next Articles

Effects of Hot Air-Vacuum Freeze Combined with Drying on Physical Properties and Prebiotic Activities of Brittle Dried Longan

DENG YuanYuan,YANG Jing,WEI ZhenCheng,ZHANG Yan,LIU Guang,ZHANG RuiFen,TANG XiaoJun,WANG JiaJia,LIAO Na,ZHANG MingWei()   

  1. Sericultural & Agri-Food Research Institute, Guangdong Academy of Agricultural Sciences/Key Laboratory of Functional Foods, Ministry of Agriculture and Rural Affairs/Guangdong Key Laboratory of Agricultural Products Processing, Guangzhou 510610
  • Received:2019-09-20 Accepted:2019-12-26 Online:2020-05-16 Published:2020-05-22
  • Contact: MingWei ZHANG E-mail:zhangmingwei@gdaas.cn

RichHTML

15

PDF

1645

Abstract:

【Objective】 The effects of hot air-vacuum freeze combined with drying (HA-VFCD) on the physical properties and prebiotic activities of high-quality brittle dried longan were investigated in the present study, so as to provide a theoretical basis for the optimal industrialized energy-saving drying mode. 【Method】 In present study, the effect of HA-VFCD on the physicochemical and nutritional characteristics, such as moisture content, water activity, shrinkage rate, water rehydration ratio, total sugar and polysaccharide contents of brittle dried longan, were compared with that of individual hot air drying (HAD) and vacuum freeze drying (VFD) longan samples. The flavor substance changes and the energy consumption were also evaluated by GC-MS and ammeter, respectively. Furthermore, the dried longan was fermented by Lactobacillus plantarum and Lactobacillus acidophilus to investigate the content changes of viable bacteria, total sugar, reducing sugar and short-chain fatty acid, thus evaluating the effect of HA-VFCD on the in vitro prebiotic activities of longan. 【Result】 Longan dried by HA-VFCD showed significantly lower moisture content, water activity and shrinkage rate, but higher rehydration ratio, compared with the HAD counterparts. The content of total sugar, polysaccharide, and the types and amounts of volatile flavor of longan dried by HA-VFCD were lower than those of VFD samples, but higher than that of HAD counterparts. In addition, HA-VFCD process could save 12.16% of drying time and 25.40% of unit energy consumption, compared with VFD process. Both Lactobacillus plantarum and Lactobacillus acidophilus could increase the number of viable bacteria through fermentation of dried longan, which were used the total sugar in dried longan to produce short-chain fatty acids and to reduce the pH of fermentation broth. And the prebiotic activities of dried longan after fermentation were remarkably affected by the drying methods and the strain types of bacteria. After fermentation by the Lactobacillus plantarumfor 48 hours, the viable bacteria number of longan dried by HA-VFCD achieved the highest value of 12.40 lg cfu/mL, which was higher than that of HAD, VFD and fresh longan samples. After fermentation by the Lactobacillus acidophilus for 48 hours, the viable bacteria number of longan dried by HA-VFCD reached 11.84 lg cfu/mL, which was close to that of VFD samples, lower than HAD samples but higher than that of fresh longan. 【Conclusion】 The HA-VFCD process combined both the advantages of HAD and VFD, which could remarkably shorten the drying time, lower the energy consumption, and improve the drying efficiency and quality of dried longan.

Key words: hot air-vacuum freeze combined with drying, longan, dried fruit, quality, prebiotic activity

Table 1

Effect of hot air-vacuum freeze combined with drying on moisture content, moisture activity and shrinkage of longan fruit"

干燥方式 Drying method 水分含量 Water content (%) 水分活度 Water activity 皱缩率 Shrinkage rate (%)
热风干燥Got air drying 14.53±0.59b 0.63±0.01b 76.43±2.13c
真空冷冻干燥Vacuum freeze drying 7.46±0.31a 0.41±0.01a 39.21±1.68a
热风-真空冷冻联合干燥
Hot air-vacuum freeze combined drying		 8.02±0.01a 0.42±0.00a 47.25±1.28b

Fig. 1

Effect of hot air-vacuum freeze combined with drying on rehydration ratio of longan fruit Different lowercase letters indicate significant difference in rehydration time of the same drying method (P<0.05); Different capital letters indicate significant difference of rehydration ratio with different drying methods at the same time (P<0.05)"

Table 2

Effect of hot air-vacuum freeze combined drying on volatile flavor substances of longan"

挥发性物质
Volatile flavor substances		 热风干燥
Hot air drying		 真空冷冻干燥
Vacuum freeze drying		 热风-真空冷冻联合干燥
Hot air-vacuum freeze combined with drying
烷烃类Alkane
三氯甲烷Trichloromethane — 0.75±0.09 0.25±0.04
十一烷Undecane 0.16±0.01 — 0.08±0.01
十二烷Dodecane 0.08±0.01 0.52±0.02 0.19±0.13
十三烷Tridecane — 0.41±0.11 0.20±0.02
十四烷Tetradecane 0.06±0.01 0.45±0.00 0.21±0.02
八甲基环四硅氧烷Octamethyl cyclotetrasiloxane — 0.18±0.11 —
十甲基环五硅氧烷Decamethyl cyclopentasiloxane 0.44±0.23 1.30±0.30 0.99±0.04
十二甲基环六硅氧烷Dodecymethyl cyclohexasiloxane 1.05±0.11 1.65±0.11 1.03±0.08
十四甲基环七硅氧烷Tetradecyclic heptasiloxane 0.69±0.11 0.86±0.06 0.54±0.01
十六烷基环八硅氧烷Hexadecyl cycloocsiloxane 0.09±0.11 0.09±0.01 0.13±0.01
正十九烷Nonadecane 0.08±0.01 — —
十八甲基环九硅氧烷Octadecymethyl cyclodoxy siloxane — 0.21±0.02 —
烷烃类总量Total alkane 2.65±0.12 6.42±0.37 3.61±0.25
烯烃类Olefin
罗勒烯异构体混合物Mixture of basil isomers 0.10±0.26 15.89±0.86 20.07±4.62
(E)-B-罗勒烯(E)-B-ocimene — 0.36±0.04 0.60±0.11
别罗勒烯Alloocimene — — 0.71±0.19
反式石竹烯Trans carnation — 0.13±0.00 0.10±0.03
古巴烯Cuba ene 0.14±0.02 —
2,6-二甲基-1,3,5,7-辛四烯2,6-dimethyl-1,3,5,7-octatetracene — — 0.13±001
α–法呢烯α–farnesene 0.16±0.02 0.19±0.02
(6E)-7,11-二甲基-3-亚甲基-1,6,10-十二碳三烯
(6E)-7,11-dimethyl-3-methylene-1,6,10-dodecatriene		 — 0.28±0.02 0.55±0.07
2,6二乙基吡嗪 2,6-diethylpyrazine — 0.55±0.05 —
2,6-二甲基-6-(4-甲基-3-戊基)双环[3.1.1]七碳-2-烯
2,6-dimethyl-6- (4-methyl-3-pentenyl)-bicyclo [3.1.1]hept-2-ene		 — — 0.11±0.03
3,7,11-三甲基-1,3,6,10-十二碳-四烯(E,E)-α-farnesene — — 0.16±0.11
烯烃类总量Total olefin 0.10±0.26 17.50±0.87 22.62±4.96
醇类Alcohol
(2R,3R)-(-)-2,3-丁二醇(R,R)-2,3-butanediol 0.39±0.07 — 0.14±0.02
2,3-丁二醇2,3-butanediol 0.72±0.24 0.92±0.05 0.14±0.01
环己醇Cyclohexanol 0.07±0.01 — —
芳樟醇Linalool — 2.03±0.34 —
苯乙醇Phenethyl alcohol — 0.37±0.04 —
醇类总量Total alcohol 1.19±0.32 3.32±0.03 0.13±0.18
酯类Ester
水杨酸甲酯Methyl salicylate 0.12±0.01 1.53±0.09 —
软脂酸乙酯Ethyl palmitate 0.07±0.00 1.05±0.03 0.07±0.02
月桂酸乙酯Ethyl laurate — 2.45±0.07 0.04±0.01
烟酸甲酯Methyl nicotinate — 1.13±0.06 —
苯甲酸乙酯Ethyl benzoate — 0.53±0.12 —
烟酸乙酯Nicotinic acid ethyl ester — 0.28±0.13 —
乙酸乙酯Ethyl acetate — 0.12±0.01 —
(Z)-3,7-二甲基-2,6-辛二烯酸甲酯
2,6-octadienoic acid,3,7-dimethyl-, methyl ester		 — 0.20±0.17 —
癸酸乙酯Ethyl caprate — 0.66±0.06 —
月桂酸甲酯Methyl laurate — 0.32±0.05 —
十四酸乙酯Ethyl myristate — 0.76±0.11 —
14-甲基十五烷酸甲酯Methyl 14-methylpentadecanoate — 0.18±0.03 —
油酸乙酯Ethyl oleate — 0.10±0.01 —
酯类总量Total ester 0.19±0.01 9.30±0.24 0.11±0.01
醛类Aldehyde
壬醛Nonanal 0.12±0.03 0.52±0.13 0.09±0.02
癸醛Capraldehyde 0.07±0.01 — —
醛类总量Total aldehyde 0.20±0.14 0.52±0.13 0.09±0.02
酸类Acid
壬酸N-nonanoic acid 0.07±0.00 — —
酸类总量Total acids 0.07±0.00 — —

Table 3

The content of total sugar and polysaccharide in longan by hot air-vacuum freezing combined with drying"

干燥方式Drying method 总糖Total sugar (mg?g-1 DW) 多糖Polysaccharide (mg?g-1 DW)
新鲜龙眼Fresh logan 1.72±0.15a 1.55±0.15a
热风干燥Hot air drying 1.86±0.09a 1.52±0.09a
真空冷冻干燥Vacuum freeze drying 3.15±0.17c 2.76±0.18c
热风-真空冷冻联合干燥Hot air-vacuum freeze combined drying 2.23±0.12b 1.96±0.13b

Table 4

Effects of hot air - vacuum freezing combined drying on energy consumption and drying time of longan fruit"

干燥方式
Drying method		 干燥2.4 kg龙眼时间Drying time of 2.4 kg longan (h) 单位能耗Unit energy consumption (mj?kg-1)
热风干燥阶段Hot air drying period 真空冷冻阶段Vacuum freeze drying period 总耗时
Total time		 热风干燥阶段Hot air drying period 真空冷冻阶段Vacuum freeze drying period 总单位能耗、Total unit energy consumption
热风干燥Hot air drying 20.00 — 20.00 7.90 — 7.90
真空冷冻干燥Vacuum freeze drying — 74.00 74.00 — 108.09 108.09
热风-真空冷冻联合干燥
Hot air-vacuum freeze combined with drying		 3.00 62.00 65.00 4.68 75.96 80.64

Fig. 2

The change of the number of viable bacteria during the fermentation of dried longan fruit by hot air-vacuum freeze combined with drying Different lowercase letters indicate significant difference among different drying methods at the same fermentation time (P<0.05). The same as below"

Fig. 3

The change of the total sugar during the fermentation of dried longan fruit by hot air-vacuum freeze combined with drying Different lowercase letters indicate significant difference of different fermentation time of the same drying method (P<0.05); * indicate significant difference between other drying methods and hot air-vacuum freeze combined drying at the same fermentation time (P<0.05). The same as below"

Fig. 4

The change of the reducing sugars during the fermentation of dried longan fruit by hot air-vacuum freeze combined with drying"

Table 5

The change of contents of short-chain fatty acids in longan fruits fermented by Lactobacillus plantarum for 48 h by hot air-vacuum freeze combined drying (μmol?mL-1)"

干燥方式
Drying method		 乙酸
Acetic acid		 丙酸
Propionic acid		 异丁酸
Isobutyric acid		 正丁酸
N-butyric acid		 异戊酸
Isovaleric acid		 正戊酸
Pentanoic acid
新鲜龙眼Fresh logan 125.92±4.38a 2.68±0.19a 0.68±0.03ab 2.65±0.09a 4.80±2.51a 0.28±0.03a
热风干燥Hot air drying 163.34±7.82c 5.61±1.02b 0.78±0.16b 6.26±0.41c 6.98±0.57ab 0.42±0.02b
真空冷冻干燥Vacuum freeze drying 157.89±2.32bc 4.65±0.52b 0.53±0.03a 4.38±0.66b 12.14±0.98b 0.41±0.01ab
热风-真空冷冻联合干燥
Hot air-vacuum freeze combined drying		 148.92±4.63b 5.90±0.75b 0.84±0.07b 3.26±0.24a 8.65±4.66ab 0.42±0.12b

Table 6

The change of contents of short-chain fatty acids in longan fruits fermented by Lactobacillus acidophilus for 48 h by hot air-vacuum freeze combined drying (μmol?mL-1)"

干燥方式
Drying method		 乙酸
Acetic acid		 丙酸
Propionic acid		 异丁酸
Isobutyric acid		 正丁酸
N-butyric acid		 异戊酸
Isovaleric acid		 正戊酸
Pentanoic acid
新鲜龙眼Fresh logan 138.18±31.16a 4.41±0.75a 0.74±0.33a 3.38±1.48ab 8.02±0.06ab 0.42±0.04a
热风干燥Hot air drying 179.08±14.05a 5.47±0.33a 0.85±0.03a 4.64±0.43b 7.60±0.26a 0.60±0.03a
真空冷冻干燥Vacuum freeze drying 145.61±24.34a 5.47±0.68a 1.41±0.07a 3.37±0.26ab 7.19±0.24a 0.49±0.09a
热风-真空冷冻联合干燥
Hot air-vacuum freeze combined drying		 177.03±27.10a 11.35±2.12b 1.80±0.34b 2.95±0.39a 9.27±1.31b 0.68±0.38a
[1] WU Y L, YI G J, ZHOU B R, ZENG J W, HUANG Y H . The advancement of research on litchi and longan germplasm resources in China. Scientia Horticulturae, 2007,114(3):143-150.
[2] 齐文娥, 陈厚彬, 彭朵芬, 晏发发 . 中国龙眼产业发展现状、问题与对策建议. 广东农业科学, 2016,43(8):169-174.
QI W E, CHEN H B, PENG D F, YAN F F . Present situation, problems and suggestions of the development of Chinese longan industry. Guangdong Agricultural Sciences, 2016,43(8):169-174. (in Chinese)
[3] 白亚娟, 刘磊, 张瑞芬, 邓媛元, 黄菲, 张名位 . 龙眼果肉提取物改善东莨菪碱诱导小鼠学习记忆功能. 中国农业科学, 2016,49(21):4203-4213.
BAI Y J, LIU L, ZHANG R F, DENG Y Y, HUANG F, ZHANG M W . Longan pulp extracts ameliorate scopolamine-induced learning and memory of impairment mice. Scientia Agricultura Sinica, 2016,49(21):4203-4213. (in Chinese)
[4] RONG Y, YANG R L, YANG Y Z, WEN Y Z, LIU S X, LI C F, HU Z Y, CHENG X R, LI W . Structural characterization of an active polysaccharide of longan and evaluation of immunological activity. Carbohydrate Polymers, 2019,213:247-256.
[5] YANG K M, CHIANG P Y . Effects of smoking process on the aroma characteristics and sensory qualities of dried longan. Food Chemistry, 2019,287:133-138.
[6] APINYAVISIT K, NATHAKARANAKULE A, MITTAL G S, SOPONRONNARIT S . Heat and mass transfer properties of longan shrinking from a spherical to an irregular shape during drying. Biosystems Engineering, 2018,169:11-21.
doi: 10.1016/j.biosystemseng.2018.01.007
[7] 陈彦林 . 不同干制方式龙眼果肉主要活性物质的比较[D]. 武汉: 华中农业大学, 2014.
CHEN Y L . Comparison of different drying methods on main active substances in longan (Dimocarpus longan Lour.) pulp[D]. Wuhan: Huazhong Agricultural University, 2014. (in Chinese)
[8] 苏东晓, 张名位, 廖森泰, 侯方丽, 张瑞芬, 唐小俊, 魏振承, 张雁, 池建伟, 邓媛元 . 龙眼果肉水溶性提取物对正常小鼠免疫调节作用的影响. 中国农业科学, 2010,43(9):1919-1925.
SU D X, ZHANG M W, LIAO S T, HOU F L, ZHANG R F, TANG X J, WEI Z C, ZHANG Y, CHI J W, DENG Y Y . Effects of water soluble extracts from longan on immune regulation in normal mice. Scientia Agricultura Sinica, 2010,43(9):1919-1925. (in Chinese)
[9] LI X, WANG L, WANG Y, XIONG Z H . Effect of drying method on physicochemical properties and antioxidant activities of Hohenbuehelia serotina polysaccharides. Process Biochemistry, 2016,51(8):1100-1108.
[10] 韩苗苗, 姚娟, 易阳, 黄菲, 王丽梅 . 龙眼果肉干燥过程中多糖的理化特征与活性变化规律. 食品科学, 2017,38(21):67-73.
HAN M M, YAO J, YI Y, HUANG F, WANG L M . Changes of polysaccharides in longan pulp during drying: Physicochemical properties and biological activities. Food Science, 2017,38(21):67-73. (in Chinese)
[11] YI Y, ZHANG M W, LIAO S T, ZHANG R F, DENG Y Y, WEI Z C, TANG X J, ZHANG Y . Structural features and immunomodulatory activities of polysaccharides of longan pulp. Carbohydrate Polymers, 2012,87(1):636-643.
[12] 王亚鸽, 支龙飞, 张益涵, 蒙源, 钟钦权, 杨志伟 . 龙眼真空冻干与热风干燥品质比较研究. 轻工科技, 2012,28(5):24-25.
WANG Y G, ZHI L F, ZHANG Y H, MENG Y, ZHONG Q Q, YANG Z W . Comparative study on quality of longan vacuum freeze-drying and hot air-drying. Light Industry Science and Technology, 2012,28(5):24-25. (in Chinese)
[13] CHUNTHAWORN S, ACHARIYAVIRIYA S, ACHARIYAVIRIYA A, NAMSANGUAN K . Color kinetics of longan flesh drying at high temperature. Procedia Engineering, 2012,32:104-111.
[14] NATHAKARANAKULE A, JAIBOON P, SOPONRONNARIT S . Far-infrared radiation assisted drying of longan fruit. Journal of Food Engineering, 2010, 100(4):662-668.
[15] 庄培荣 . 龙眼肉微波真空干燥技术的研究[D]. 福州: 福建农林大学, 2011.
ZHUANG P R . Studies on the microwave vacuum drying of arillus longan[D]. Fuzhou: Fujian Agricultural and Forestry University, 2011. (in Chinese)
[16] 田玉庭, 陈洁, 李淑婷, 庄培荣, 庄玮婧, 郑宝东 . 不同干燥方法对龙眼果肉品质特性的影响. 西北农林科技大学学报(自然科学版), 2012,40(8):161-165.
TIAN Y T, CHEN J, LI S T, ZHUANG P R, ZHUANG W J, ZHENG B D . Effect of different drying methods on the quality of longan (Dimocarpus longan Lour.) pulp. Journal of Northwest Agriculture and Forestry University (Natural Science Edition), 2012,40(8):161-165. (in Chinese)
[17] RAJKUMAR G, SHANMUGAM S, GALVAO M D S, DUTRA-SANDES R D, LEITE-NETA M T S, NARAIN N, MUJUMDAR A S . Comparative evaluation of physical properties and volatiles profile of cabbages subjected to hot air and freeze drying. LWT-Fodd Scienceand Technology, 2017,80:501-509.
[18] SZYCHOWSKI P J, LECH K, SENDRA-NADAL E, HEMNANDEZ F, FIGIEL A, WOJDYLO A, CARBONELL-BARRACHINA Á A . Biocompounds, antioxidant activity, and sensory attributes of qui