2023 年 29 巻 2 号 p. 147-153
This study investigated the effects of enzymatic treatments on yuzu (Citrus junos) squeezed juice residue under low temperature by adding small amounts of enzyme solutions on paste yields, and their volatile compositions. Yuzu juice residue was enzymatically degraded by adding different volumes of enzyme solutions to residue to obtain paste. The yield of paste was 68.1% in the treatment of adding equal amounts of enzyme solutions to residue for 5h at 40 °C. In the treatments of adding 10 % or 5 % (v/w, based on the weights of the wet residue) volume of enzyme solution to residue for 24h at 10 °C, yields of paste were 67.6 % or 67.1 % (dry matter base), respectively. In enzymatic treatments of adding 10 % or 5 % (v/w, based on the weights of the wet residue) volume of enzyme solutions to residue at 10 °C, pastes were obtained without the processes of heating and separating the water. Degraded residue was strained with a spatula by hand to obtain paste in those treatments, because it was not necessary to separate the water from the mixture due to the small amount of enzyme solution that was added. Relative percentages of the volatile components of α-pinene, σ-elemene, decanal, β-elemene, and γ-cadinene were higher in the paste enzymatically treated at 10 °C than in the paste treated at 40 °C.
Yuzu (Citrus junos) is a popular sour citrus fruit in Japan. In Hiroshima Prefecture, yuzu is cultivated mainly in the north area, and yuzu juice is used for both drinks and fruit vinegar. Yuzu juice residue is a byproduct of extracting juice from whole yuzu fruits, and it is composed of flavedo, albedo, segment membranes, and seeds. According to a yuzu juice factory in Hiroshima Prefecture, when a yuzu fruit is juiced, about 80 % of a single yuzu fruit becomes yuzu juice residue. However, most yuzu juice residue is composted, and is not used for food. To increase the use of yuzu juice residue for food, it is necessary to make it easy to use.
Previous reports have discussed attempts at extracting sugars or organic acids from orange peel waste using pectinase and cellulase (Wilkins et al., 2005), as well as at improving the juice yield from bael fruit using pectinase (Singh et al., 2012). We thought that if yuzu juice residue could be made into paste, we could easily use it, for example, as paste added to confectioneries, bread, or various foods. Yuzu has a large amount of pectin in the peel which comprises a major part of the dietary fiber (Kuwada et al., 2012). Therefore, we intended to use pectinases to make juice residue into paste and tried to develop a simple method of making paste from yuzu juice residue using enzyme treatments.
At low temperatures, enzyme activity is low (Ezugwu et al., 2014), and it takes more time to degrade subjects than at high temperatures. There are some reports of liquefaction of apple pomace (Will et al., 2000) and improved juice yield (Singh et al., 2012) using pectinases, but we could not find reports comparing the effects of different volumes of enzyme solution on paste yield. Because yuzu juice residue contains about 80 % water, it could be degraded by adding only a small amount of enzyme solution under low temperature, and paste could be obtained by straining the degradant without separating the water. This method could eliminate the processes of heating and mixing, and water separation. If unground yuzu juice residue could be enzymatically degraded, seeds of yuzu juice residue could be removed from the paste by straining the degradant in this method because they are not degraded by pectinase.
In this study, aiming to develop a simple method for making paste, we investigated the effects of different enzymatic treatments on yuzu juice residue on paste yields, and their volatile compositions. In Experiment 1, we obtained basic data on the degradation of yuzu juice residue and yields of paste using pectinase at 40 °C by adding an equal amount of enzyme solutions to residue. In the subsequent experiment (Experiment 2), we tried to degrade yuzu juice residue by adding 10 % (v/w, based on the weights of the wet residue) or less enzyme solution to residue at 10 °C. In Experiment 3, we used unground yuzu juice residue, assuming the actual production process, and we aimed to remove seeds. It has been reported that volatile compositions of yuzu cold-pressed oil changed between different temperatures of storage (Njoroge et al., 1996). The volatile compositions were compared between pastes enzymatically treated at 40 °C and at 10 °C to evaluate the effects of the degradation temperature on volatile compositions.
Materials Yuzu juice residue was obtained from a yuzu juice factory in Hiroshima Prefecture. Whole yuzu fruits were cultivated in November 2018, and juice was extracted using a belt press. About 80 % of a single yuzu fruit became yuzu juice residue, and yuzu juice residue contains about 80 % water. Yuzu juice residue was stored at −20 °C until tested. In Experiments 1 and 2, yuzu juice residue was ground using a food processor (Panasonic, MK-K81) before enzymatic treatment. In Experiment 3, unground yuzu juice residue was used. Three different commercial pectinases were examined. Sumizyme SPG (mainly comprised of polygalacturonase, activity of 150 000 u/g) and sumizyme PTE (mainly comprised of pectin trans-eliminase, activity of 125 u/g) were obtained from SHIN NIHON CHEMICAL Co., Ltd. (Japan), and macerozyme 2A (mainly comprised of protopectinase, activity of 8 000 u/g) was obtained from Yakult Pharmaceutical Industry Co., Ltd. (Japan).
Experiment 1Enzymatic degradation by adding equal amounts of enzyme solutions to residue Yuzu juice residue was enzymatically degraded by adding equal amounts of enzyme solutions to residue. Twenty mL of a 0.4 % enzyme solution dissolved in distilled water was added to 20 g of ground yuzu juice residue. The final enzyme concentration of the mixture was 0.2 %. The pH of the mixture was 3.3 to 3.4. Enzymatic treatment was done at 40 °C in capped 50 ml PP bottles shaken reciprocally at 100 rpm for 5h. After enzymatic treatment, the mixtures were heated in water at 80 °C for 30 min for enzyme inactivation, and samples were centrifuged (1 370 × g, 10 °C, 10 min) to separate precipitate and supernatant. Precipitate was strained using a strainer with a 355 µm pore size and a plastic spatula to obtain paste and separate un-degraded residue and seeds. The yield of paste was calculated by dividing the wet weights of the strained, degraded residue by the wet weights of the precipitate. The concentration of galacturonic acid in the supernatant was analyzed by HPLC. The conditions of HPLC analysis were as follows: column; Aminex HPX-87H (300 × 7.8 mm), column oven temperature; 50 °C, eluent; 5 mM H2SO4, flow rate; 0.5 mL/min, detector; refractive index (RI-2031-plus, JASCO), injection volume; 10 µL. The sample's concentration of galacturonic acid was calculated by comparing it against the area of the standard D-galacturonic acid (Wako Pure Chemical Corporation (Japan)).
Experiment 2Enzymatic degradation by adding less than 10 % volume of enzyme solutions to residue Yuzu juice residue was enzymatically degraded by adding 10 % (v/w, based on the weights of the wet residue) volume of enzyme solutions to residue to select an enzyme at 10 °C.
Afterward, the effects of different volumes of enzyme solutions on residue were examined using selected enzymes. Enzymatic degradation of residue was performed by adding 10 %, 5 %, 2.5 %, and 0 % (only enzyme powder) (v/w, based on the weights of the wet residue) volume of enzyme solutions to residue. Zero % volume of enzyme solution means that the enzyme was not dissolved in water and only enzyme powder was added to the residue.
The final enzyme concentration of mixtures of residue and enzyme solution was 0.2 %. Mixtures were allowed to stand at 10 °C for 24h. After enzymatic treatment, mixtures were heated in water at 80 °C for 30 min for enzyme inactivation, and strained using a strainer as in Experiment 1. The yields of paste were calculated by dividing the wet weights of the strained, degraded residue by the wet untreated residue, subtracting the added solution. In the comparison of effects of different volumes of enzyme solution, the yields of paste were calculated using the dry matter weight.
Experiment 3Enzymatic degradation by adding 5 % volume of enzyme solutions to unground residue Fifteen mL of enzyme solution was added to 300 g of unground yuzu juice residue and sealed in pouches made of nylon/LDPE (low density polyethylene). The final enzyme concentration of the mixture was 0.2 %. Enzymatic treatment was performed by keeping the pouches at 10 °C for 24h or at 40 °C for 3h. The processes of enzyme inactivation and straining the paste are same as in Experiment 2. The analysis of the volatile components of the yuzu pastes and residue was done by GC and GC-MS.
Extraction of volatile components of yuzu pastes and yuzu juice residue by SPME The volatile components of each yuzu paste and residue were extracted by solid phase micro extraction (SPME). SPME fiber (Supelco, 50/30 µm DVB/CAR/PDMS) was used for extraction. Samples (pastes and homogenized yuzu juice residue, 0.1 g) were equilibrated at 50 °C for 20 min in a 10 mL vial, and extracted at 50 °C for 3 min prior to injection to GC or GS-MS. Homogenization of yuzu juice residue was conducted using a homogenizer (Nissei, AM-7) under freezing by liquid nitrogen. SPME fiber was injected into injection port of the GC or GC/MS in splitless mode. Extracted volatile components were desorbed by the carrier gas (helium, flow rate 1 mL/min (25.6 cm/s)) and cryofocused on the capillary column with liquid nitrogen for 7 min. The GC and GC-MS analyses are described below.
Analysis of volatile components of yuzu pastes and yuzu juice residue GC analysis was carried out to compare relative peak area percentages of the detected volatile components among treatments by using a Shimadzu GC-2010 Plus gas chromatograph equipped with a flame ionization detector (FID) and DB-WAX capillary column (J&W Scientific, 60 m × 0.25 mm i.d., 0.25 µm film thickness). The initial column temperature was 40 °C, which was then increased at 3 °C/min to 230 °C, and then held for 20 min. Helium was the carrier gas with a flow rate of 1 mL/min (25.6 cm/s). The injection port and detector temperatures were at 240 °C. The analyses were performed on each treatment of 3 samples.
GC-MS analysis was carried out to identify compounds by using a Varian 220-MS connected with a Varian 450-GC, under the same GC conditions as those of the GC-2010 Plus. Mass spectra were obtained from m/z 20 to 500 at a scan speed of 0.5 sec/scan with an ionization voltage of 70 eV. Identification of compounds detected by GC-MS was performed by comparison of mass spectra and Kovats retention indices (RI) with the standards that had been previously analyzed, and with the NIST 08 Mass Spectral Library. Retention indices were calculated by using a homologous series of n-alkanes (C7 to C25).
Statistical analysis The experimental data are expressed as the mean ±SD. The statistical analysis was performed by Tukey's multiple range test. Experiments were triplicated.
Experiment 1 Pectin is a main part of the dietary fiber in yuzu (Kuwada et al., 2012). Pectinases used in this report were selected based on their ability for the degradation of tissues and relatively low temperature for enzyme inactivation. Other reports have discussed changes in the volatile composition of yuzu cold-pressed oil during storage (Njoroge et al., 1996). Deterioration of the volatile components of yuzu could be suppressed in lower temperatures.
Three different pectinases were tested. Yuzu juice residue was degraded by adding equal amounts of enzyme solution to residue at 40 °C. Yields of paste of each enzyme treatment are shown in Table 1. Concentrations of galacturonic acid of the supernatants are shown in Table 2.
| Pectinases | 0.5h | 1h | 2h | 3h | 5h |
|---|---|---|---|---|---|
| SPG | 58.2 ± 6.4a | 63.2 ± 4.2a | 65.0 ± 1.2a | 64.2 ± 5.2a | 68.1 ± 3.3a |
| PTE | 26.6 ± 1.8b | 36.5 ± 2.8b | 43.4 ± 2.7b | 50.3 ± 5.3b | 56.5 ± 5.1b |
| 2A | 33.3 ± 2.9b | 37.0 ± 3.5b | 53.0 ± 2.4c | 55.6 ± 2.8b | 60.3 ± 2.4b |
Values shown are yields of paste after enzymatic treatment by adding equal amounts of enzyme solutions to yuzu juice residue.
Values are expressed as the mean ± SD.
Means with different letters are significantly different at the same time (p < 0.05).
| Pectinases | 0.5h | 1h | 2h | 3h | 5h |
|---|---|---|---|---|---|
| SPG | 0.19 ± 0.01 | 0.25 ± 0.01a | 0.38 ± 0.02a | 0.49 ± 0.01a | 0.63 ± 0.01a |
| PTE | ND | 0.03 ± 0.00b | 0.06 ± 0.01b | 0.08 ± 0.00b | 0.11 ± 0.00b |
| 2A | ND | ND | ND | ND | ND |
Yuzu juice residue was degraded by adding equal amounts of enzyme solutions.
Values are expressed as the mean ± SD.
Means with different letters are significantly different at the same time (p < 0.05).
ND: Not detected
Yields of paste increased as time passed. Concentrations of galacturonic acid also increased in the treatments of sumizyme SPG and sumizyme PTE, but this increase was not observed with macerozyme 2A. Yields of paste and concentrations of galacturonic acid were higher with SPG than with other pectinases (p < 0.05). Pectin is composed of galacturonic acid (Flutto, 2003), and galacturonic acid was released by the pectinase. Enzymatic liquefaction of apple pomace under the condition of adding an equal amount of enzyme solution to pomace has been reported (Will, 2000). In that report, concentrations of galacturonic acid increased proceeding enzymatic degradation of the apple pomace, and the concentrations were different among enzymes. SPG is mainly composed of polygalacturonase. It is possible that the release of galacturonic acid and degradation of yuzu juice residue occurred more easily with SPG than with other enzymes.
Concentration of galacturonic acid increased in fully ripe fruit (Wilkins et al., 2005). The pectin content of Assam lemons decreased with the advancement of fruit maturity (Mukhim et al., 2016). In this experiment, yuzu juice residue was generated from ripened yuzu. Degradation of residue may have proceeded more easily than with unripe yuzu because of its low pectin content.
Experiment 2 In Experiment 1, yuzu juice residue was degraded by adding equal amounts of enzyme solution to residue and shaking at 40 °C. In this way, the processes of shaking the mixture under heat and separating the water by centrifuging to create the paste are necessary. However, it is difficult for small food manufacturers to install new equipment. Therefore, we tried to develop a simple method for making paste from yuzu juice residue without the processes of thermal shaking and removing the water.
As yuzu juice residue is about 80 % water, we thought that residue could be degraded by adding a small amount of enzyme solution, and paste could be obtained after degradation by straining using a strainer and spatula, without removing the water. The process of straining degradant is also able to remove seeds.
The progresses of degradation by adding 2 ml of enzyme solution to 20 g of residue at 10 °C are shown in Table 3, and they were similar to those of Experiment 1. The yield of paste treated without enzymes (with only water added) for 24h was 13.7±1.5 %. Yields of paste were higher in the treatments of sumizyme SPG than of sumizyme PTE and macerozyme 2A at 6h, 16h, and 24h, respectively (p < 0.05). Yields of paste after 16h and 24h with SPG were 69.3 % and 68.5 %, respectively. Enzymatic treatment at low temperatures may have an effect of decreasing deterioration of heat-sensitive components.
| Pectinases | 6h | 16h | 24h |
|---|---|---|---|
| SPG | 60.8 ± 3.0a | 69.3 ± 2.6a | 68.5 ± 3.5a |
| PTE | 32.1 ± 5.3b | 37.0 ± 3.0b | 42.5 ± 2.0b |
| 2A | 31.5 ± 1.0b | 44.9 ± 4.5b | 55.4 ± 3.9c |
Values shown are yields of paste after enzymatic treatment by adding 10 % (v/w, based on the weights of the wet residue) volume of enzyme solution to residue.
Values are expressed as the mean ± SD.
Means with different letters are significantly different at the same time (p < 0.05).
The progresses of degradation by sumizyme SPG adding different volumes of enzyme solution to residue are shown in Table 4. Yields of paste in treatments of adding 10 % or 5 % (v/w, based on the weights of the wet residue) volume of enzyme solution for 24h at 10 °C were 67.6 % or 67.1 % (dry matter base), respectively, and they were higher than that in the treatment of adding 0 % (v/w, based on the weights of the wet residue) volume of enzyme solution (only enzyme) (p < 0.05). Based on this result, it is possible that adding water increased the opportunity for binding enzymes and substrates and promoted enzymatic degradation.
| Volume of SPG solution | ||
|---|---|---|
| (%, v/w) | 6h | 24h |
| 10% | 57.6 ± 4.4 | 67.6 ± 3.9a |
| (58.2 ± 2.6) | (72.2 ± 3.9) | |
| 5% | 57.6 ± 4.1 | 67.1 ± 3.9a |
| (58.0 ± 2.1) | (73.1 ± 5.2) | |
| 2.5% | 56.3 ± 2.6 | 59.4 ± 2.7ab |
| (58.0 ± 1.2) | (66.9 ± 2.7) | |
| 0% (only enzyme) | 52.9 ± 4.8 | 55.6 ± 3.8b |
| (57.1 ± 4.0) | (63.7 ± 2.3) |
Values shown are yields of paste after enzymatic treatment by adding different volumes (%, v/w, based on the weights of the wet residue) of enzyme solution to residue.
Yields are calculated as dry matter weight. Figures in ( ) are yields of paste calculated as fresh matter weight subtracting the weight of the added solution.
Values are expressed as the mean ± SD.
Means with different letters are significantly different at the same time (p < 0.05).
Wilkins et al. (2005) reported that enzymatic hydrolysates of orange peel waste contained sugars and organic acids. This simple method also has an effect for utilizing these substances, because the supernatant and precipitate did not need to be separated.
Experiment 3 In this experiment, the volume (v/w, based on the weights of the wet residue) of enzyme solutions was set to 5 %, because the yields of paste enzymatically treated by adding 5 % (v/w) volume of enzyme solution were more than 67 % (dry matter base) in Experiment 2 and we were able to obtain paste with less water content than that by adding 10 % volume of enzyme solution. Also, we used unground yuzu juice residue, assuming the actual production process.
Yields of paste were 76.7 ± 5.6 % when enzymatically treated at 10 °C for 24hr and 73.9 ± 2.2 % when treated at 40 °C for 3hr, similar to Experiment 2. There was no significant difference in the yields of paste between treatments. This result suggests that the process of grinding yuzu juice residue before enzymatic treatment is not needed. Because seeds were not degraded and remained as they were, seeds were able to be removed by straining degradants in this method. Citrus seeds have limonoids (Hasegawa et al., 1980), and present bitterness (Dea et al., 2013). The ability to remove seeds has a valuable effect on improving taste because limonoids have strong bitterness (Hasegawa et al., 1980). In this study, bitterness was not evaluated. Further research is needed to estimate the taste of the paste obtained by straining the degradant.
To evaluate the volatile compositions of each sample, we compared the relative volatile compositions of the pastes enzymatically treated at different temperatures and yuzu juice residue. There was no significant difference in the total peak area between treatments and residue.
Thirty volatile compounds were detected and the relative compositional changes between samples were compared (Table 5). Fourteen monoterpene hydrocarbons, 6 sesquiterpene hydrocarbons, 5 alcohols, 3 aldehydes, 1 monoterpene oxide, and 1 ester were detected from yuzu pastes and yuzu juice residue. The most abundant component of the paste treated at 10 °C was limonene at 66.2 %, followed by γ-terpinene at 11.3 % and linalool at 5.3 %. The main relative compositions were similar to those in previous reports (Lan et al., 2008, Akakabe et al., 2008).
| № | RI | Compound | Paste 10°C | Paste 40°C | Yuzu juice residue |
|---|---|---|---|---|---|
| 1 | 1026 | α-pinene | 0.59 ± 0.05a | 0.49 ± 0.03b | 0.55 ± 0.01ab |
| 2 | 1029 | α-thujene | 0.18 ± 0.01 | 0.16 ± 0.02 | 0.18 ± 0.01 |
| 3 | 1104 | β-pinene | 0.45 ± 0.03 | 0.42 ± 0.02 | 0.48 ± 0.01 |
| 4 | 1115 | Sabinene | 0.06 ± 0.00ab | 0.04 ± 0.01a | 0.07 ± 0.00b |
| 5 | 1159 | Myrcene | 1.96 ± 1.02 | 2.59 ± 0.21 | 2.07 ± 0.92 |
| 6 | 1163 | α-phellandrene | 0.41 ± 0.71 | 0.33 ± 0.04 | 0.55 ± 0.96 |
| 7 | 1185 | α-terpinolene | 0.26 ± 0.13a | 0.53 ± 0.06b | 0.37 ± 0.11ab |
| 8 | 1215 | D-limonene | 66.16 ± 1.49 | 64.37 ± 0.54 | 65.85 ± 0.42 |
| 9 | 1220 | β-phellandrene | 2.54 ± 0.11 | 2.71 ± 0.26 | 2.72 ± 0.03 |
| 10 | 1224 | (E)-2-hexenal | 0.04 ± 0.01 | 0.05 ± 0.01 | 0.04 ± 0.01 |
| 11 | 1237 | (Z)-β-ocimene | 0.07 ± 0.02 | 0.25 ± 0.11 | 0.17 ± 0.01 |
| 12 | 1256 | γ-terpinene | 11.28 ± 1.89 | 11.94 ± 0.73 | 11.70 ± 0.20 |
| 13 | 1277 | p-cymene | 1.23 ± 0.05 | 1.53 ± 0.18 | 1.39 ± 0.04 |
| 14 | 1290 | terpinolene | 0.80 ± 0.02 | 0.84 ± 0.09 | 0.76 ± 0.00 |
| 15 | 1293 | octanal | 0.01 ± 0.00a | 0.04 ± 0.01b | 0.02 ± 0.01ab |
| 16 | 1359 | 1-hexanol | 0.05 ± 0.01a | 0.09 ± 0.00b | 0.10 ± 0.01b |
| 17 | 1376 | Alloocimene | 0.03 ± 0.01 | 0.05 ± 0.01 | 0.04 ± 0.00 |
| 18 | 1390 | (Z)-3-hexenol | 0.08 ± 0.01a | 0.12 ± 0.01b | 0.12 ± 0.01b |
| 19 | 1455 | Linalool oxide | 0.02 ± 0.00 | 0.03 ± 0.01 | 0.01 ± 0.00 |
| 20 | 1483 | σ-elemene | 0.14 ± 0.01a | 0.09 ± 0.02b | 0.01 ± 0.00c |
| 21 | 1510 | Decanal | 0.09 ± 0.01a | 0.04 ± 0.03b | 0.09 ± 0.01a |
| 22 | 1558 | Linalool | 5.29 ± 0.82a | 6.53 ± 1.06ab | 7.71 ± 0.37b |
| 23 | 1567 | 1-octanol | 0.03 ± 0.01 | 0.04 ± 0.00 | 0.04 ± 0.00 |
| 24 | 1601 | β-elemene | 0.11 ± 0.01a | 0.08 ± 0.01b | 0.06 ± 0.00b |
| 25 | 1614 | Caryophyrene | 0.58 ± 0.09 | 0.74 ± 0.08 | 0.59 ± 0.02 |
| 26 | 1670 | β-farnesene | 0.55 ± 0.05a | 0.35 ± 0.13ab | 0.27 ± 0.02b |
| 27 | 1706 | Terpinyl acetate | 0.86 ± 0.12a | 0.89 ± 0.06a | 0.52 ± 0.03b |
| 28 | 1769 | σ-cadinene | 0.18 ± 0.02 | 0.12 ± 0.03 | 0.10 ± 0.01 |
| 29 | 1773 | γ-cadinene | 0.05 ± 0.01a | 0.03 ± 0.01b | 0.03 ± 0.00b |
| 30 | 1807 | Nerol | 0.04 ± 0.01a | 0.05 ± 0.01a | 0.02 ± 0.00b |
| Total (%) | 94.16 | 95.54 | 96.66 |
Values are expressed as the mean ± SD.
Means with different letters are significantly different in same compound (p < 0.05).
Comparing the pastes treated at 10°C and 40 °C, relative peak area percentages of α-pinene, σ-elemene, decanal, β-elemene, and γ-cadinene were higher in the paste treated at 10°C than in the paste treated at 40 °C (p < 0.05), while α-terpinolene, octanal, 1-hexanol, and (Z)-3-hexenol were lower in paste treated at 10 °C than in the paste treated at 40°C (p < 0.05). Relative peak area percentages of nerol were higher in the paste treated at 10 °C and 40 °C than in the residue (p < 0.05), and sabinene was lower in the paste treated at 40 °C than in the residue (p < 0.05).
Changes in the volatile composition of yuzu cold-pressed oil during storage have been examined (Njoroge et al., 1996). In that report, the relative percentage of the terpenes, limonene, γ-terpinene, myrcene, terpinolene, α-terpinene, α-pinene, and β-sabinene decreased under storage at 20 °C compared to -21 °C and 5 °C, while the alcohols, linalool and nerol, the sesquiterpenes, β-elemene, γ-elemene, and β-farnesene increased under storage at 20 °C. Considering their report, it seems that the differences of relative peak area percentages of α-pinene, sabinene, and nerol among treatments are due to heating during the enzymatic treatment.
Relative peak area percentages of octanal were higher in the paste treated at 40 °C than in the paste treated at 10 °C (p < 0.05); however, decanal was higher in the paste treated at 10 °C than in the paste treated at 40 °C (p < 0.05). On the other hand, the linalool in residue was higher than that of the paste treated at 10 °C (p < 0.05). These results suggest that other factors had affected the volatile compositions.
We investigated the effects of enzymatic treatments on yuzu (Citrus junos) juice residue under low temperature adding small amounts of pectinase enzyme solutions on paste yields, and their volatile compositions. Yuzu juice residue was degraded by adding 10 % (v/w, based on the weights of the wet residue) or less volume of enzyme solution and the mixture was allowed to stand at 10 °C. Paste could be obtained by straining the degradant with a spatula by hand. Yields of paste were 67.6 % or 67.1 % (dry matter base) in enzymatic treatments of adding 10 or 5 % (v/w, based on the weights of the wet residue) volume of enzyme solution for 24h at 10 °C, respectively.
The relative percentages of volatile components of paste were estimated. The differences of relative peak area percentages of α-pinene, sabinene, and nerol among treatments suggest that the temperature of enzymatic treatment influenced volatile compositions.
Conflict of interest There are no conflicts of interest to declare.
