第27卷第6期农业工程学报V ol.27 No.6
2011年6月 Transactions of the CSAE Jun. 2011 337 Effects of high hydrostatic pressure processing on quality of
yellow peaches in pouch
Zhang Fusheng1,2, Zhao Jun1,2, Chen Fang1,2, Liao Xiaojun1,2,
Wang Zhengfu1,2, Wu Jihong1,2※, Hu Xiaosong1,2
（1.College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China;2. Chine National Engineering Rearch Centre for Fruits and Vegetables Processing, Key Laboratory of Fruits and Vegetables Processing, Ministry of Agriculture, Engineering Rearch Centre for Fruits and Vegetables Processing, Ministry of Education, Beijing 100083, China）
Abstract: In order to expand the application of non-thermal processing in canned fruits industry, the effects of high hydrostatic pressure (HHP) processing on qualities of yellow peaches in pouch (YPP) was investigated, and subquently texture, microstructure, color,pH value, titratable acidity(TA), and total soluble solid (TSS) of HHP procesd YPP were evaluated and compared to thermal procesd o
ne. The results showed that texture, microstructure, color, pH value, TA, and TSS of YPP treated by HHP processing (600 MPa, >5 min) were prerved, while texture and microstructure of YPP treated by thermal processing (90±2°C, 20 min) were vere damaged and TSS incread. Sensory evaluation of HHP procesd YPP showed no significant differences from unprocesd samples in nsory attributes except for taste and freshness, while thermal processing had significant effect on nsory attributes except for color and aroma. The result can provide a reference for industrial production of HHP procesd canned fruits.
Key words: texture, color, nsory evaluation, yellow peaches in pouch (YPP), high hydrostatic pressure (HHP)
doi：10.3969/j.issn.1002-6819.2011.06.059
CLC number：TS255.3 Document code：A Article ID：1002-6819(2011)-06-0337-07
Zhang Fusheng, Zhao Jun, Chen Fang, et al. Effects of high hydrostatic pressure processing on quality of yellow peaches in pouch[J]. Transactions of the CSAE, 2011, 27(6): 337－343. (in English with Chine abstract)
张甫生，赵 君，陈 芳，等. 高静压加工对黄桃罐头品质的影响[J]. 农业工程学报，2011，27(6)：337－343.
0 Introduction
Yellow peach in pouch (YPP) is very popular as one of the canned fruits in many countries, and the consumption of YPP increas steadily. The global canned peach (about 70% yellow peach) consumption was about 1.0 million metric tons per year[1]. YPP was generally sterilized by conventional heating methods to ensure the safety of products and to extend shelf life. However, the detrimental changes in the organoleptic qualities of YPP, especially the softening of flesh often occurred. Therefore, food scientists and manufacturers were continuously arching for novel processing techniques to destroy undesired microorganisms and improve product quality[2-3].
Over the last decade, high hydrostatic pressure (HHP) processing has been proven to be an effective non-thermal
Received date：2011-04-21 Revid date：2011-06-10
Foundation items: National Natural Science Foundation of China (No.30972067); Municipal Science and Technology Program of Beijing, China(No. 10110504660000).
Biography: Zhang Fusheng, Ph.D candidate, majored in non-thermal processing of fruits and vegetables. College of Food Science and Nutritional Engineering, China Agricultural University, Beijing, 100083, China.
Email:*********************
※Corresponding author: Wu Jihong, Ph.D, vice-professor, majored in fruits and vegetables processing. College of Food Science and Nutritional Engineering, China Agricultural University, Beijing, 100083, China.
Email:**************** pasteurization technique in fruit processing[4], in which food was subjected to pressures up to 600 MPa and initial temperatures lower than 40°C for veral minutes[5], resulting in the inactivation of bacteria, yeasts and moulds[6]. Moreover, the detrimental changes in texture, color, and nsory properties of fresh fruits could be avoided, such as strawberry halves[3], melon pieces[7], apple cubes[8] and pineapple slices[9]. However, there was little study on the effects of HHP on canned fruits, which were generally blanched for inactivating indigenous enzymes.
Bad on the microbial and enzymatic inactivation, the objective of this work was to evaluate the effects of HHP on qualities of YPP with comparison of thermal processing (TP), including texture, col
or, pH value, TA, TSS, and nsory attributes, so as to provide some information for industrial production of HHP procesd canned fruits .
1 Materials and methods
1.1 Preparation of yellow peaches in pouch
Fresh yellow peaches (cv. Guanwu) were provided by Fomdas Food Co. (Zhejiang, China). The peach fruits were harvested at commercial maturity from a local peach plant orchard on July 21, 2009 and stored at 4±1°C. The pretreatment procedure of fresh yellow peaches was carried out in the company as follows: peaches were halved, manually cored with half-round knives, peeled by spraying 90 g/L NaOH solution at 90°C, washed with running water
农业工程学报2011年338
immediately, sliced, blanched at 91±2°C for 6 min, cooled to
<25°C by running water immediately, and placed in plastic pouches (EVOH/PVPP, 227 mL). Eight or nine sliced peaches (about 130 g) were packaged in each pouch, and then boiled syrup (≥85°C) with 240 g/L sugar and 0.2 g/L citric acid was filled into each pouch. The pouches were vacuum aled (0.
04 MPa) immediately, cooled to 25°C by running water within 30 min, and then stored at 4±1°C for further HHP processing within 12 h.
咋发朋友圈1.2 High hydrostatic pressure processing and thermal processing
HHP processing was carried out in a medium-size HHP apparatus (Baotou Kefa High Pressure Technology Co., Ltd, Inner Mongolia, China). The apparatus was equipped with two individual 100 L horizontal vesls. Water was ud as the pressure transmitting fluid. Bad on previous experiment, HHP processing (600 MPa, ≥5 min) can inactivate bacteria, molds and yeasts, YPP (50 pouches each time) were procesd by HHP at 600 MPa for 5, 10, and 30 min, respectively. The initial temperature of sample was about 20°C, and temperature was lower than 40°C during HHP processing. Traditional thermal processing of YPP was carried out in a thermostatic water bath (LY-9A, Qingyuan Science & Technology Development Co. Ltd., Beijing, China) and held at90±2°C for more than 20 min. Then, samples were immediately cooled to room temperature by running water.
After HHP and TP processing, the tissues of YPP for microstructure analysis were put into fixative (glutaraldehyde solution) immediately. Texture and color were measured within 24 h. Viscosity of syrup, pH value, TA, TSS, and nsory evaluations were analyzed two days later so that syrup could
distribute uniformly. Samples for pectin fractions were kept at -20°C until analysis. Samples without HHP and TP processing were stored at 4°C as unprocesd control. All quality evaluations were carried out
at 25±2°C and in triplicate.
1.3 Microbiological analysis
Total aerobic bacteria, moulds and yeasts counts of YPP were conducted according to the method of Bull et al.[6]钻石戒子
25 mL of sample was added to 225 mL of sterile 8.5 g/L sodium chloride solution for 1.5 min in an electromechanical blender (JYL-B060, Joyong Electric Appliance Co., Shandong, China). Aliquots were rially diluted with sterile 8.5 g/L sodium chloride solution and 1.0 mL of diluted (or non-diluted) samples was plated into duplicated plates of appropriate agar. Total aerobic bacteria were conducted using plate count agar (PCA). Moulds and yeasts counts were conducted using ro bengal agar (RBA). Plates were incubated for 5 d at 27°C for yeasts and moulds counts and 24 h at 37°C for aerobic bacteria prior to counting. Microbial counts were expresd as Log10 cfu/mL.
1.4 Texture analysis
Samples of YPP were equilibrated to room temperature before textural analysis. Texture was a multi-parameter attribute[10]. The parameter considered in this study was hardness. Texture profile analysis (TPA) was ud to evaluate YPP texture by using a texture analyzer (TA-XT2i, Stable Micro System, UK). Samples cut from the slices (10 mm width × 10 mm length × 5 mm height) on transversal line were placed on the ba plate of TA-XT2i with a cylindrical aluminum probe (50 mm in diameter) using a 25 kg load cell. The crosshead pre-test, test and post-test speed was 1 mm/s, with a rest period of 5 s between cycles and the deformation was 60% of the original height[11]. At least 20 samples were measured individually and an average hardness value was calculated.
1.5 Microstructure analysis
A subction (1 cm×1 cm×0.5 cm) was excid from original sample using a razor blade. This subction was further reduced to 1 mm3 cubes. The cubes were fixed in 4% (v/v) glutaraldehyde solution (0.1 mol/L phosphate buffer, pH value 7.2, at 4°C, 24 h), post-fixed with 20 g/L OsO4 (2 h), dehydrated using a graded ethanol ries (50%(v/v), 70%, 80%, 95% and 100%) for 20 min each[12]. The dehydrated samples were subjected to a critical point device (Balzers CPD 030, Canonsburg, PA, USA) using CO2 as transition agent. Samples were fixed on steel supports and then sputter-coated with gold using a JEOL metalizer (JEE-420, Tokyo, Japan). Samples were obr
ved in a scanning electron microscope (Hitachi, S3400N, Tokyo, Japan) at 20 kV.
1.6 Viscosity measurement of YPP syrup
Viscosity of YPP syrup was determined using an AR550 rheometer (TA Instruments, Waters Co., Ltd., Surrey, Great Britain) with a conical end concentric cylinder (stator radius = 15.00 mm, rotor radius = 14.00 mm, immerd height = 42.00 mm, vertical gap = 5920 µm). 13.5 mL syrup was applied at each measurement with 25 ± 0.1°C controlled by circulating water in a thermostatic system. In the test, the shear rate was incread from 4 to 63 s−1, and the average data was ud as viscosity value in this paper[13].
1.7 Preparation and determination of pectin fractions
Cell wall material was isolated as described by Ro et al.[14], and then pectin fractions were fractionated from the cell wall material by using the methods of Sila et al.[15] with some modifications. Cell wall material (50 mg) was extracted quentially with 20 mL of 50 mmol/L sodium acetate buffer at pH value 6.5 at 25°C (4 h), 20 mL of 50 mmol/L EDTA at pH value 6.5 and 25°C (6 h), and 20 mL of 50 mmol/L Na2CO3 containing 20 mmol/L NaBH4 at 4°C (16 h) followed by 6 h at 28°C under continuous shaking. Extracts were centrifuged at 15 000 g for 15 min at 4°C to recover t
he insoluble material for further u. Each step was repeated in triplicate and the supernatants were collected as water soluble pectin (WSP), chelator soluble pectin (CSP) and sodium carbonate soluble pectin (NSP).
The water soluble pectin in syrup (syrup WSP) was extracted by the method described by IFUMA[16]. All collected pectin fractions were made up to 100 mL with distilled water. Pectin content was determined by the carbazole method[17], and results were expresd as milligrams of galacturonic acid per gram fresh weigh (FW).
第6期张甫生等：高静压加工对黄桃罐头品质的影响339
1.8 Color measurement
Color measurement was conducted at 25°C, using a SC-80 color difference meter (Kangguang Co., Beijing, China) in a reflectance mode. The L*, a*, b* color space was ud for determination of the color, with L* reprenting the lightness, +a* the red direction, −a* the green direction, +b* the yellow direction, and −b* the blue direction. Samples of yellow peach flesh and syrup were filled into a glass sample pouch and placed under the aperture of the color difference meter. The L*, a* and b*value of samples were measured and the total color differences (∆E) were calculated using the following equ
ation[18], where L*0, a*0, and b*0 are the values of unprocesd samples.
∆E= [(L*-L*0)2 + [(a*-a*0)2 + [(b*-b*0)2]1/2
1.9 Physicochemical characteristics analysis
1.9.1 Determination of pH
pH value was measured at 25°C with a thermo Orion 868 pH meter (Thermo Fisher Scientific, Inc., MA, U.S.A), which was calibrated with pH 4.0 and pH 7.0 buffer. The pH value of flesh was measured by juice extruded from them, and the pH value of syrup was measured directly.
1.9.2 Determination of titratable acidity (TA)
An aliquot of sample (10 g or 10 mL) was titrated using 0.1 mol/L sodium hydroxide (Sinopharm Chemical Reagent Beijing Co., Ltd, Beijing, China) to the t end point (pH = 8.2±0.1) by an automatic tetrameter (851 GPD titrino, Metrohm, Switzerland). The volume of sodium hydroxide was converted to milligram citric acid[19], and the results were expresd as gram of citric acid per kilogram FW.
1.9.3 Determination of total soluble solid (TSS)
螃蟹可以冷冻保存吗
TSS was determined by using a WAY-2S digital Abbe refractionmeter (Shanghai Precision and Scientific Instrument Co., Shanghai, China) at 25°C. The TSS value of flesh was measured by juice extruded from them, and the TSS value of syrup was measured directly.
1.10 Sensory evaluations
Sensory evaluations of the YPP were carried out by 10 trained panelists comprising of staffs and graduate students from the College of Food Science and Nutrition Engineering, China Agricultural University. A descriptive analysis technique was ud to asss qualities of YPP. YPP were opened 5 min before running the tests, and peach slices were put in white plastic rving dishes. All samples were coded with three-digit numbers at random. The panelists were instructed to score each attribute such as chewiness, hardness, taste, freshness, color, aroma and overall acceptability on a 5-point hedonic scale in which 1 denoted dislike extremely and 5 denoted like extremely[20].
1.11 Statistical analysis
All the values provided were the average of triplicate (or more than triplicate). To determine the significant differences of the results, an analysis of variance (ANOVA) and Tukey’s test was carried out with confidence level of 95% (p≤0.05), using the software Microcal Origin 7.5 (Microcal Software,
Inc., Northampton, U.S.A). 2 Results and discussion
2.1 Effect on inactivation of microorganisms
The total aerobic bacteria, yeasts and moulds counts in
YPP after HHP and TP processing were determined. The
initial counts of total aerobic bacteria, yeasts and moulds in unprocesd YPP were 4.5 and 4.3 Log10 cfu/mL, respectively.
The initial counts in this study were lower than in a previous
study[21], since blanching treatment caud an approximately
2 Log reduction of microorganisms. As shown in Table 1,
both thermal and HHP processing resulted in inactivation of
all microorganisms to a level below the detection limit. HHP processing at 600 MPa for 5 min is sufficient to produce
党建指导员
YPP with microbiological safety.房地产基础知识
Table 1 Microbiological result of YPP treated by HHP and
TP processing
Treatment conditions
Total aerobic bacteria/
(Log10 cfu·mL-1)
Yeasts and Molds/
(Log10 cfu·mL1)
Control 4.5
4.3 600 MPa, 5 min,10 min, 30min N.D.* N.D.
TP processing (90±2°C, 20 min)N.D. N.D. Note: *N.D.: not determined
2.2 Effect on texture
2.2.1 Effect on texture of YPP flesh
The hardness of YPP after HHP and TP processing was
shown in Fig.1. The hardness of unprocesd YPP was 87.4
N, the hardness of HHP procesd YPP did not show significant difference regardless of increasing pressure-
holding time, indicating that HHP could retain the hardness
of YPP. However, the hardness of thermal procesd YPP decread by 65%, indicating TP processing caud the softening of YPP with deleterious texture changes. This
result was similar to what Nguyen et al.[4] propod that
HHP processing (600 MPa, 25°C, 5 min) improved texture retention while TP processing (105°C, 5 min) led to texture softening of carrot and jicama.
乡村医生刘旭
罗兴汉
Texture of fruits and vegetables was largely determined
by pectic substances in the cell wall[22-23], and many previous
studies had testified that thermal softening was mainly due
to non-enzymatic depolymerized reaction of the cell wall
pectin[15,23]. A typical non-enzymatic depolymerized reaction
often resulted in the decreasing of insoluble pectin fraction
(NSP and CSP), and the increasing of soluble pectin fraction
老龟(total WSP, including flesh WSP and syrup WSP)[23].
In order to validate the typical non-enzymatic depolymerized reaction, pectin compositions contents of both thermal and
HPP procesd YPP were determined and showed in Fig.2.
YPP after TP processing exhibited a significant decreasing
in NSP and CSP, and a significant increasing in total WSP
as expected, indicating that TP processing promoted depolymerized reaction in YPP and led to the flesh softening.
YPP after HHP processing regardless of pressure-holding
time was characterized with no significant changes in NSP,
CSP and total WSP,suggesting that HHP inhibited the depolymerized reaction and prerved the texture. The
results well agreed with the texture analysis.
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340
Note: values were means ± standard deviations (n = 10), error bars reprented standard deviation of the means, different letters in the bars indicated significant differences at p <0.05.
Fig.1 Effect of HHP and TP processing on hardness of YPP
Note: values were means ± standard deviations (n = 3), error bars reprented standard deviation of the means, different letters in the bars indicated significant differences at p < 0.05.
Fig.2 Effect of HHP and TP processing on pectin fractions of
YPP
2.2.2 Effect on viscosity of YPP syrup
Viscosity is one of the textural attributes of edible syrup which highly affect the preference of consumers [24-25]. Viscosity of syrup in all treatments displayed a shear- thinning type of behavior in the shear rate range between 4 and 63 s -1 (Fig.3), suggesting that syrup followed the non-Newtonian flow behavior. This result was similar to what Krebbers et al.[26] propod, in which HHP or TP processing didn’t change the flow behavior of tomato puree. However, Viscosity of thermal procesd syrup was significantly higher than that of HHP procesd and unprocesd syrup, which could be attributed to the leaching of some WSP into syrup during the processing [27]. HHP processing also caud pectin leaching, but the effect was limited, which is probably due to the tighter cell structure and inhibition of pectin depolymerization [4].
In addition, as compared with unprocesd YPP, although viscosity of syrup treated by HHP showed smaller fluctuations with increasing pressure-hold time, there was no significant difference (data are showed in Table 3), indicating that
pressure-hold time did not affect syrup viscosity.
Note: values were means ± standard deviations (n = 3), error bars reprented standard deviation of the means.
Fig.3 Viscosity of syrups in YPP against shear rate for HHP and
TP processing
2.2.3 Effect on microstructure of YPP flesh
The microstructures of the unprocesd, HHP procesd and thermally procesd YPP samples were prented in Fig. 4. The unprocesd YPP cells were almost isodiametrical and polyhedral as well as distributed uniformly throughout the matrix, demonstrating less intracellular space between cells.
The comparison of the microstructure (Fig. 4 a-d) of unprocesd and HHP procesd YPP, showed the size of the cell became smaller than that of the control sample obviously, which indicated the cellular structure was more compact and benefited for flesh texture. Furthermore, the application of HHP resulted in an improvement in cell-to- cell contact, and which incread as pressure hold time prolonging. On the other hand, thermal procesd YPP showed more structural damages (Fig.4 e). After TP processing, the YPP cell was swelled or broken. This might be due to the degradation of pectin during TP processing. Similar results were reported for cooked carrots [15], and cell wall paration and the erosion of middle lamella were also found in thermal procesd strawberries [3].
This obrvation agreed with the texture data in Fig.1, supporting that HHP processing prerved texture, while TP processing damaged texture.
2.3 Effect on color
The effects of HHP and TP processing on the color of YPP are given in Table 2. For peach flesh, L *, a * and b * values were not significantly different among HPP, thermal procesd and unprocesd samples. For the syrup, as compared to that of unprocesd YPP, L * and a * values were not significantly affected, but b * values incread significantly in all treatments, most probably due to the diffusion of yellow color pigments following the disruption of the cellular structure. In addition, the b * value of HHP procesd syrup exhibited a decreasing tendency with increasing pressure-hold time. This was probably due to hindering dissolution and diffusion of yellow pigment from peach fleshes, the mechanisms of which were not clear, but may related to tighter cellular structure caud by increasing
第6期张甫生等：高静压加工对黄桃罐头品质的影响341
pressure-hold time.
A lot of studies had suggested that a noticeable color change could be visualized when ∆E was over 2[13]. Compared with unprocesd samples, the ∆E values of fleshes and syrup in all treatments were less than 2, indicating that neither HHP nor TP processing resulted in visible color changes. Noticeable color differences had occurred after blanching pretreatment[28-29].
a. Control
b. 600 MPa, 5
min
c. 600 MPa, 10 min
d. 600 MPa, 30 min
e. TP
Fig.4 Scanning electron micrographs of cortex tissue of YPP after HHP and TP processing (×150 times)
Table 2 Color of YPP treated by HHP and TP processing
Flesh Syrup
Processing
conditions L*a*b*∆E L*a*b*∆E Control 56.87±0.74a 6.04±0.15a 45.04±0.04a 0 57.52±0.04a 1.44±0.08a -2.30±0.10c 0 5min 55.72±1.23a 5.85±0.21a 45.03±0.04a 1.1756.78±0.01a 1.28±0.06a -1.70±0.10a 0.96 10min 55.50±1.70a 6.53±0.50a 45.27±0.91a 1.4757.07±0.26a 1.27±0.10a -1.70±0.10a 0.77 30min 55.48±1.36a 6.40±0.65a 44.65±0.44a 1.7757.07±0.83a 1.36±0.05a -1.97±0.15b 0.56 TP 56.20±0.18a 6.58±0.06a 44.26±0.82a 1.1657.44±0.08a 1.30±0.04a -2.00±0.01b 0.34 Note: values are means ± standard deviations, n = 3, different letters within a column indicate significant differences at p < 0.05.
2.4 Effect on pH, TA, and TSS
The effects of HHP and TP processing on some other
physical and chemical properties of YPP are shown in Table
3. For both flesh and syrup, the pH and TA contents showed
small fluctuations, but did not increa or decrea
significantly after HHP or TP processing. Li et al[30]
obrved similar results about the change of pH value and
TA contents in pineapple juices after HHP processing. The
TSS of HHP procesd YPP was not significantly different
from unprocesd YPP, but was significantly lower than that
of thermal procesd YPP. The result could be attributed to
the solubilization of more carbohydrates, such as sugar and
pectin, due to the disruption of cell structure by thermal
processing[4]. Besides, the TSS of fleshes was higher than
that of the syrup, probably ascribing to more carbohydrates
solubilization after crushing.
Overall, pH, TA, and TSS were well prerved after
HHP processing. This could be considered as a benefit of the
non-thermal condition of HHP as compared to conventional
thermal techniques.
Table 3 pH, TA, and TSS of YPP treated by HHP and TP processing
pH TA/(g·kg-1) TSS/(g·L-1)
Processing
conditions Flesh Syrup Flesh Syrup Flesh Syrup
Viscosity/(mPa·s) Control 3.45±0.005a 3.39±0.003a 4..32±0.09a 3.60±0.09a 172.0±2.9b 146.3±3.8b 5.13±0.17b
5 min 3.45±0.003a 3.35±0.003a 4..24±0.05a 3.48±0.09a 170.7±1.9b 149.3±1.5b 5.18±0.18b
10 min 3.45±0.013a 3.36±0.002a 4.26±0.09a 3.62±0.01a 168.0±1.5b 152.0±2.0b 5.16±0.27b
30 min 3.47±0.010a 3.39±0.003a 4.27±0.06a 3.65±0.08a 167.3±2.9b 150.0±03.6b 5.15±0.31b
TP 3.48±0.005a 3.44±0.008a 4.17±0.13a 3.59±0.09a 185.7±1.9a 166.0±2.0a 11.76±0.50a
Note: values are means ± standard deviations, n = 3, different letters within a column indicate significant differences at p < 0.05.
