2019 年 25 巻 4 号 p. 577-585
Pandan leaf extract, a major source of 2-acetyl-1-pyrroline (2AP), encapsulated in rice starch aggregates was investigated to improve shelf life for its pleasant flavor and color by spray drying a mixture of non-glutinous or glutinous rice starch, gum acacia, and fresh pandan leaf extract under various conditions. An increase in the amount of pandan leaf extract resulted in a darker green color with a larger amount of chlorophyll. Scanning electron microscopy observation revealed that the microstructure of the product consisted of spheres with an average diameter of 34.14–50.98 µm. The spray dry process, which comprises high temperature treatment of the mixture matrices, caused a change in the pasting properties, as compared with native starch. Quantitative determination of 2AP realized using headspace SPME-GC-MS-SIM revealed that rice starch aggregates are able to entrap 2AP. Encapsulated 2AP was released into the headspace with rice starch gelatinization.
The microencapsulation technique is of particular interest to food technologists because of its enormous potential for the controlled release of an encapsulated ingredient at the right place and the right time. Food substances that are commonly encapsulated include food additives and a broad range of food ingredients. Encapsulation ensures delivery of the optimum dosage and stability (Gouin, 2004), and also decreases the effects of chemical degradation, evaporation, and oxidation (Kausadikar et al., 2015), thereby improving cost effectiveness. Of these characteristics, flavor can constitute the most valuable ingredient in any food formula and must be protected as it is usually delicate and volatile. Therefore, preserving the flavor under specific conditions until use is a major concern for food manufacturers (Madene et al., 2006) due to its relationship with the quality and acceptability of food products. However, foodstuffs containing synthetic flavors are often avoided because of concerns about toxicity or damage to health (Teixeira et al., 2004). Accordingly, natural flavor has become a requirement, but the amount of potent flavor is difficult to control. Among natural volatile compounds, 2-acetyl-1-pyrroline (2AP), a major component of aromatic rice, has been reported as an important odorant in numerous foods (Buttery et al., 1982; Schieberle and Grosch, 1987; Hofmann et al., 1998). The compound is of great interest to the flavor industry, as it can be found in plants, particularly pandan, Pandanus amaryllifoloius Roxb. leaf, which is one of the best natural sources of 2AP (Laohakunjit and Kendchoechuen, 2007). 2AP is typically described as having a pleasant nutty, aromatic rice-like, popcorn-like aroma with an odor threshold value of as low as 0.1 ppb in water (Yahya et al., 2011). Pandan leaf extract is commonly used as a food coloring and flavoring agent in many traditional foods and drinks, particularly in Southeast Asian countries, including Thailand (Rattanapitigorn et al., 2016; Yahya et al., 2010; Ping et al., 2014). However, fresh pandan leaf extract deteriorates quickly and its flavor changes. In general, the processing of any active or volatile compound into a solid phase through encapsulation could provide a more stable form, leading to a long shelf life and convenience (Reineccius, 1991). Many studies have examined the protection or stabilization of 2AP, including through the use of coating, encapsulation, and complexation technologies. Apintanapong and Noomhorm (2003) used spray drying to encapsulate 2AP obtained by the steam distillation of pandan leaf extract and using a mixture of gum acacia and maltodextin as a carrier material. They reported that 30% of the 2AP had degraded after 35 days of storage. Laohakunjit and Kerdchoechuen (2007) stabilized 25% pandan leaf extract by supercritical fluid extraction, with a 30% sorbitol-plasticized rice starch film and further demonstrated a potential application by coating non-aromatic rice to impart the 2AP aroma. The coated rice was packed in plastic bags (nylon15 / PE20 / LLDPE75) and stored at 25 °C for 6 months. The products showed that the 2AP aroma was retained in the coated non-aromatic rice, thus implying that 2AP coating could help to improve rice aroma. Andreas et al. (2012) also reported the encapsulation of pandan leaf extract by spray drying with maltodextrin and β-cyclodextrin as a wall material; the powder product was used for enhancing roasted notes, thus masking off-odors in lipids and oils in foods. Yin and Cadwallader (2018) reported the entrapment of 2AP by complexing it with zinc ions using spray chilling with lipids to protect the moisture. This product demonstrated high stability of 2AP at room temperature (25 °C) for up to 3 months.
Various substances can be employed for encapsulation, and starch is widely used because it can form an inclusion complex with small molecules, including flavor. However, the interaction between aroma compounds, which typically bring taste and flavor, and carbohydrates, is generally weak in terms of energy and mainly depends on the nature and concentration of the aroma compound and carbohydrates (Andreas et al., 2012). Many traditional confectionaries and desserts in Southeast Asia, including Thailand, frequently use rice flour or rice starch as their main ingredients and some incorporate fresh pandan leaf extract for coloring and flavor. Both items play important roles in consumer satisfaction and influence further consumption of the food. However, the processes for extracting juice from fresh pandan leaves are very complicated and time consuming, and the extract has a short shelf life. The instability of color and flavor was influenced by the storage environment, i.e., light, temperature, or oxidation (Madene et al., 2006), and has led to a demand for converting the perishable extract to a stable form with convenient properties for dessert production. As many rice-based desserts are popular in Southeast Asian countries, rice starch was selected because it naturally contains small particles and has the ability to combine into potentially useful porous spheres (Zhao and Whistler, 1994; and Surojanametakul et al., 2005), which may be able to entrap the natural flavor from pandan leaves.
The aim of the present work was to encapsulate 2AP, a potent flavor compound, and chlorophyll, the natural green color in the fresh pandan leaf extract, in the structure of rice starch aggregates prepared from rice starch mixed with a binding agent such as gum acacia, to extend shelf life and control flavor release. The physicochemical properties of the resulting powder products were also evaluated with regard to their practical industrial use.
Materials Non-glutinous (amylose content 21.16 ± 0.77%) and glutinous rice starches (amylose content 2.01 ± 0.51%) were purchased from Bangkok Starch Industries Co. Ltd. (Bangkok, Thailand). The amylose content was determined using Amylose/Amylopectin Assay Kit (K-AMYL, Megazyme, Bray, Ireland), and the procedure was performed in accordance with the kit instructions. The food grade binding agent gum acacia (Luxara 3A Gum Acacia) was supplied by Arthur Branwell Co. Ltd. (Essex, UK). Fresh pandan leaves were purchased from a Thai local market.
2-Acetyl-1-pyrroline and a 13C-labeled compound, 2-acetyl-(13C-methyl)-1-pyrroline were prepared according to the method described by Yoshihashi et al. (2002). The 2AP concentration was determined by comparing the 1H-NMR signal with that of ethanol. Other chemicals used were of analytical grade and obtained from Wako Chemicals (Osaka, Japan).
Preparation of aqueous pandan leaf extract 1.0, 1.5, and 2.0 kg of fresh pandan leaves were separately washed, drained, and cut into small pieces (2 mm thick). Sliced leaves were then mashed in 3 L of water using a high-speed electrical blender (Buono, Guangzhou, China). The mixture was filtered through a nylon cloth (300 mesh) to remove leaf residue. Filtrates were collected for later use, and the extract was used within 2 h.
Encapsulation of pandan leaf extract with rice starch aggregate Rice starch aggregate was prepared as described by Surojanametakul et al. (2005). Either non-glutinous (RRS) or glutinous rice starch (GRS) containing 24% solids (w/w) was individually dispersed into a homogenized mixture of 0.30% (w/w) gum acacia and aqueous pandan leaf extract containing 10%, 15%, and 20% (w/w), giving a 10-L solution. The mixed solution was then sprayed through a spray gun at a rate of 1 L/3 min in a commercial spray dry unit (Niro Atomize series 7526; Copenhagen, Denmark) with inlet and outlet temperatures in the 230–280 °C and 75–90 °C ranges, respectively. The powder was retrieved from the collection chamber and used for further evaluation. All the experiments were conducted in triplicate.
Color and chlorophyll content The color of the sample powder was measured as L* (lightness/darkness coordinate), a* (red/green coordinate), and b* (yellow/blue coordinate) using a color reader (Spectraflash SF 600 plus; Datacolor, Lawrenceville, NJ).
The chlorophyll content was determined by the AOAC method (1990) with a minor modification, as described below. One gram of powdered sample was accurately weighed, and then extraction was performed with 85% (v/v) acetone. The extract was filtered, and the residue was washed and filtered again until all the color was extracted. The extract was diluted for colorimetry with 85% (v/v) acetone, and absorbance (Abs.) was measured at 660 and 642.5 nm using a UV/visible spectrophotometer (UV-1700; Shimadzu, Kyoto, Japan). The total chlorophyll content was calculated (7.12 Abs. 660 nm + 16.8 Abs. 642.5 nm) and the values were converted to a mg/g powder product.
Particle size distribution Particle size distribution was measured using Mastersizer S (Malvern Panalytical Ltd., Malvern, UK) with a He-Ne laser source at λ 633 nm with a beam length of 2.40 mm, and air as a dispersing medium. Distribution was calculated with a refractive index as 1.5300.
Cohesiveness property The cohesive property was evaluated using the texture analyzer model TA XT plus (Stable Micro Systems Ltd., Hamilton) equipped with a helical blade. A sample of approximately 140 mL (70 mm in height) was placed in a beaker and then measured to determine its flow characteristics using the Quick Test program. The average compaction and cohesion values were recorded. The cohesive index of each sample powder was expressed as flow behavior by comparison with the cohesive index (CI) according to Abdullah et al. (2010), wherein the samples were divided into five categories: extremely cohesive (CI >19), very cohesive (CI = 16–19), cohesive (CI = 14–16), easy flowing (CI = 11–13), and free flowing (CI <11).
Microstructure Dehydrated powder samples were placed in a vacuum evaporator, which was attached to an aluminum stub with carbon tape and coated with gold (Ion coater IB-2, Eiko, Japan). Samples were analyzed in a scanning electron microscope (SEM) (JSM-5600 LV; JEOL, Tokyo, Japan) operating at an accelerating voltage of 10 kV, as reported by Sánchez et al. (2002).
Pasting property The pasting properties of all powdered samples were determined using a Rapid Visco Analyzer (RVA) (RVA-super 3; Newport Scientific, New South Wales, Australia) according to the AACC International Approved Method 61-02.01 (AACC, 2000). The sample (3.0 g, weighted as 12% moisture basis) was mixed and dispersed in 25 mL of distilled water prior to performing the analysis on the RVA. The mixture was stirred at 960 rpm for 10 s, and then the rate was changed to 160 rpm. The paste was held at 50 °C for 1 min and heated at a constant rate (12 °C/min) to 95 °C. After that, it was held at 95 °C for 2.5 min, cooled at a constant rate (12 °C/min) to 50 °C, and finally held at 50 °C for 2.1 min. An RVA profile of paste viscosity versus time was plotted, and used to determine the peak, final, breakdown, and setback viscosities.
Moisture, protein contents, and Aw The moisture and protein contents of the encapsulated powders were measured following AOAC (1990), while water activity (Aw) was measured with a water activity instrument (Novasina, Lachen, Switzerland).
Quantitative analysis of 2AP content of powder A headspace analysis of 2AP was performed using solid phase micro extraction (SPME) with the stable isotope dilution method. A 10-mL SPME vial with a screw cap (18-09-1306; Shimadzu, Japan) was used for headspace extraction. A sample (0.75 g) was added to saturated brine (3.038 mL) and 0.2 M phosphate buffer pH 8.0 (0.332 mL) that was filled with water to 6.75 mL. The final concentration of 20 ppb of 13C labeled 2AP was an internal standard. 2AP was extracted into a headspace with the auto-sampler program (AOC-5000; Shimadzu, Kyoto, Japan) at room temperature or 80 °C, which induced sample gelatinization, for 10 min. SPME was performed during the headspace extraction with SPME fiber, divinylbenzene-carboxen-polydimethylsiloxane (57328-U; Supelco, Bellefonte). The fiber was then exposed to an injector maintaining a temperature of 200 °C. GC-MS (GCMS-QP2010, Shimadzu, Kyoto, Japan) analysis was performed with DB-WAXetr (60 m × 0.25 mm ID × 0.25 µm film thickness; Agilent, Santa Clara). The MS interface and MS ion source temperatures were set at 200 °C and 220 °C, respectively. The GC oven temperature program ranged from 50 °C (5 min) to 260 °C (5 min) at a rate of 10 °C/min. Helium was used as a carrier gas, and the linear velocity was set at 51.1 cm/s. M/z 111 and 112, which represent 2AP and 13C-labeled 2AP as an internal standard, were monitored with the SIM mode. Quantification was performed by comparing the 2AP and 13C-labeled 2AP peak areas with a calibration curve. The analysis was performed in duplicate.
Storage stability Sample powders were kept in sealed metalized PET bags and stored at room temperature (∼30 °C) for 10 weeks. The sample used for quantifying the 2AP content was determined using SPME-GC-MS with an 80 °C extraction temperature. The reduction of 2AP in all the powder samples after storage for 10 weeks was calculated.
Data analysis All experiments were carried out in triplicate, except 2AP quantitative analysis. Results are reported as average values with standard deviations. Analysis of variance (ANOVA) and Duncan's multiple range test (DMRT) at P = 0.05 were used to determine the differences between treatments.
Color and chlorophyll content of the products All the products were green with a typical pandan leaf extract flavor; these characteristics play a very important role in consumer acceptance. As the concentration of pandan leaf extract increased, a higher b* was observed in the product, while the L* and a* values tended to become lower (Table 1). This suggests that a higher content of pandan leaf extract provided a greener and darker color, and the present content could successfully encapsulate chlorophyll in the extract. Among the samples, the lowest a* value was found in rice starch aggregates entrapping 20% pandan leaf extract. Generally, the green color reflected the retention of chlorophyll in the extract. The total chlorophyll content of the products varied in the 0.10–0.32 mg/g range (Figure 1). The chlorophyll content increased following pandan leaf extract. Chlorophyll was easily degraded to pheophytin with dilute acids, heat, light, or oxygen (Tonucci and Von Elbe, 1992; Erge et al., 2008), and this resulted in color deterioration from bright green to olive brown (Ryan-Stoneham and Tong, 2000; Koca et al., 2006; Ping et al., 2014) due to the heat and spray drying process. The encapsulated products presented here could conserve the green color caused by chlorophyll from the pandan leaf extract that might be entrapped with rice starch and gum acacia, and thus reduced the loss during the spray drying process. All products exhibited low moisture content and Aw, as shown in Table 2, which was expected to improve storability.
| Sample | Color value | ||
|---|---|---|---|
| L* | a* | b* | |
| RRS + 10%PLE | 92.84 ± 0.06 a | −5.12 ± 0.14 d | 12.16 ± 0.01 d |
| RRS + 15%PLE | 90.80 ± 0.14 c | −6.35 ± 0.07 c | 15.28 ± 0.02 c |
| RRS + 20%PLE | 87.65 ± 0.11 e | −7.32 ± 0.02 ab | 19.28 ± 0.06 a |
| GRS + 10%PLE | 91.10 ± 2.26 b | −6.35 ± 0.61 c | 15.16 ± 2.59 c |
| GRS + 15%PLE | 88.23 ± 0.06 d | −7.18 ± 0.04 b | 18.90 ± 0.06 b |
| GRS + 20%PLE | 88.39 ± 0.27 d | −7.44 ± 0.06 a | 18.88 ± 0.11 b |
Note: Different letters in the same column indicate statistical differences (p < 0.05) by DMRT. RRS means non-glutinous rice starch, GRS means glutinous rice starch, PLE means aqueous pandan leaf extract.
Total chlorophyll content of rice starch aggregates with pandan leaf extract.
Note: RRS means non-glutinous rice starch, GRS means glutinous rice starch, PLE means aqueous pandan leaf extract.
| Sample | Moisture (%) | Aw | Particle size (µm) |
|---|---|---|---|
| RRS | 10.30 ± 0.12 a | 0.57 | 40.42 ± 1.16 c |
| RRS + 10%PLE | 6.35 ± 0.04 c | 0.22 | 46.85 ± 2.72 b |
| RRS + 15%PLE | 5.21 ± 0.04 f | 0.15 | 38.83 ± 1.54 cd |
| RRS + 20%PLE | 6.64 ± 0.01 b | 0.17 | 35.92 ± 0.66 de |
| GRS | 10.19 ± 0.01 a | 0.57 | 27.46 ± 0.99 f |
| GRS + 10%PLE | 5.09 ± 0.38 f | 0.12 | 50.98 ± 3.25 a |
| GRS + 15%PLE | 5.76 ± 0.14 e | 0.18 | 34.14 ± 0.26 e |
| GRS + 20%PLE | 5.94 ± 0.03 d | 0.2 | 45.53 ± 3.47 b |
Different letters in the same column indicate statistical differences (p < 0.05) by DMRT. RRS means non-glutinous rice starch, GRS means glutinous rice starch, PLE means aqueous pandan leaf extract.
Particle size The particle sizes (average sphere diameters) of the non-glutinous and glutinous rice starches were 40.42 and 27.46 µm, respectively. The results revealed that their particle sizes varied in the 35.92–46.85 µm range in non-glutinous rice starch aggregates and in the 34.14–50.98 µm range in glutinous rice starch aggregates. However, the addition of pandan leaf extract had less effect on the particle sizes of the product, as shown in Table 2.
Flow behavior of the products The flow behavior of the products was also evaluated to determine whether it was free flowing or cohesive and, therefore, did not flow as readily. Knowing the powder flowability could help to prevent production stoppages during bulk solid handling. Generally, the flow properties of particulate solids depend on various factors, i.e., size, shape, size distribution of the particles (Durney and Meloy, 1986), moisture content, and time-consolidation (Bodhmage, 2006). In this experiment, all encapsulated products exhibited different flow behaviors ranging from easy flowing to extremely cohesive (Table 3). It was found that the flowability of the products differed significantly depending on the type of starch and the amount of pandan leaf extract added (p < 0.05), as shown in Table 3. Products with a high content of natural pandan leaf extract (20%) exhibited poor flowability in terms of cohesive index, as mentioned by Abdullah et al. (2010). The products obtained from non-glutinous rice starch with 10 and 15% pandan leaf extract flowed easily when compared with glutinous rice starch-based aggregates with the same amount of pandan leaf extract. Surprisingly, aggregates from non-glutinous rice starch with 20% pandan leaf extract exhibited the poorest flowability (extremely cohesive). Among the samples, glutinous rice starch aggregates with 15% pandan leaf extract had the highest compaction coefficient, while non-glutinous rice starch aggregates with 10% pandan leaf extract showed the lowest value. The high compaction coefficient reflected the fact that the powder was less stable during the compression process.
| Sample | Compaction coefficient (g, mm) |
Cohesion coefficient (g, mm) |
Cohesive Index (mm) |
Flow Behavior |
|---|---|---|---|---|
| RRS + 10%PLE | 2915.95 ±153.05 b | 791.47 ± 39.9 c | 13.15 ± 0.61 c | Easy Flowing |
| RRS + 15%PLE | 3155.71 ± 228.71 ab | 749.47 ± 41.10 c | 12.46 ± 0.66 c | Easy Flowing |
| RRS + 20%PLE | 3338.49 ± 25.31 ab | 1153.05 ± 29.78 a | 19.16 ± 0.44 a | Extremely cohesive |
| GRS + 10%PLE | 2942.70 ± 142.89 b | 831.98 ± 23.10 c | 13.86 ± 0.37 c | Easy Flowing |
| GRS + 15%PLE | 3539.45 ± 254.08 a | 949.01 ± 64.50 b | 15.79 ± 1.02 b | Very Cohesive |
| GRS + 20%PLE | 3318.99 ± 223.36 ab | 1021.38 ± 25.13 b | 16.97 ± 0.38 b | Very Cohesive |
Note: Compaction and cohesion coefficients were determined by the method of Abdullah et al. (2010), where the blade up through the sample column during the decompression phase at 50 mm/sec. Different letters in the same column indicate statistical differences (p < 0.05) by DMRT. RRS means non-glutinous rice starch, GRS means glutinous rice starch, PLE means aqueous pandan leaf extract.
Pasting properties The pasting properties of the products measured by RVA are shown in Table 4. The RVA profile of non-glutinous rice starch had the highest gelatinization temperature, indicating that it is the least easily cooked among the samples. All the encapsulated products revealed that the starch portions experienced some changes during the spray dry process and heating; however, the pasting properties remained, even in the spray dried products. The type of starch and the amount of pandan leaf extract affected the pasting properties of the products. Rice starch aggregates commonly had a lower gelatinization temperature and showed higher peak viscosity, breakdown, and setback than native starch. Surprisingly, the final viscosity and setback viscosity of glutinous rice aggregates increased, which was in contrast to non-glutinous rice starch products. In this experiment, glutinous rice starch aggregates provided faster and easier cooking, but resulted in softer gel (lower setback viscosity) than non-glutinous rice starch aggregates. The results also revealed that the amount of pandan leaf extract had less effect on the pasting properties of the products, whereas the pasting properties of native starch, glutinous or non-glutinous, had a greater effect.
| Sample | Gelatinization temperature (°C) |
Peak viscosity (RVU) |
Breakdown (RVU) |
Final viscosity (RVU) |
Setback (RVU) |
|---|---|---|---|---|---|
| RRS | 81.7 ± 0.07 a | 262 ± 2.24 f | 90.8 ± 1.41 c | 270.7 ± 3.41 a | 99.3 ± 0.07 c |
| RRS + 10%PLE | 66.2 ± 2.45 c | 354 ± 3.30 a | 230.3 ± 34.94 a | 221.9 ± 13.17 a | 132.9 ± 16.47 b |
| RRS + 15%PLE | 67.4 ± 0.07 bc | 378 ± 10.96 a | 225.3 ± 8.66 a | 213.9 ± 0.96 a | 164.2 ± 11.93 a |
| RRS + 20%PLE | 65.6 ± 0.33 c | 353 ± 2.00 a | 223.6 ± 20.68 a | 210.8 ± 5.36 a | 143.1 ± 7.37 b |
| GRS | 68.7 ± 0.00 b | 273 ± 0.28 e | 153.2 ± 0.88 b | 147.5 ± 0.05 d | 27.6 ± 0.23 d |
| GRS + 10%PLE | 63.3 ± 0.18 d | 343 ± 3.30 bc | 199.0 ± 7.57 a | 163.9 ± 4.91 c | 180.1 ± 1.61 a |
| GRS + 15%PLE | 63.2 ± 0.01 d | 321 ± 5.35 d | 195.3 ± 8.10 a | 151.1 ± 1.41 cd | 170.9 ± 6.76 a |
| GRS + 20%PLE | 62.5 ± 0.53 d | 334 ± 0.23 a | 202.4 ± 3.41 a | 153.1 ± 0.53 cd | 181.7 ± 0.76 a |
Note: Different letters in the same column indicate statistical differences (p < 0.05) by DMRT. RRS means non-glutinous rice starch, GRS means glutinous rice starch, PLE means aqueous pandan leaf extract.
Scanning electron microscopy (SEM) The microstructure of rice starch aggregates containing various amounts of pandan leaf extract is shown in Figure 2. SEM morphological observation of the starch aggregates revealed various numbers of starch granules, the sizes and shapes of granules packed together, and granules loosely packed. Mainly, the powder microstructure consisted of spheres and regular shapes, which agrees with the findings of Zhao and Whistler (1994) and Surojanametakul et al. (2005). The pandan leaf extract concentration had no effect on the appearance of starch aggregates.
Microstructure of rice starch aggregates with pandan leaf extract.
2AP concentration in aggregates A high 2AP content was released from the rice starch aggregate at 80 °C with gelatinization. This was approximately 5–8 times higher than the release of 2AP at room temperature (Figure 3). At 80 °C, starch was gelatinized, causing the complex structure of starch and 2AP to collapse (Yoshihashi et al., 2005), then 2AP was released. A greater amount of encapsulated 2AP was observed in samples with a greater amount of encapsulated pandan leaf extract. On the other hand, rice starch type had less influence with regard to encapsulating 2AP in their structure (Figure 3). Therefore, amylose content may not be a major factor influencing encapsulation, even though the amylose fraction is expected to have the ability to form complex or inclusion compounds with a variety of ligands including aroma compounds (Heinemann et al., 2003; Nuessli et al., 1995; Tietz et al., 2008). With respect to our results, non-glutinous rice starch aggregates with 20% pandan leaf extract had the highest 2AP content (1 393 ppb), followed by glutinous rice starch aggregate with 20% pandan leaf extract (1 245 ppb). Accordingly, both rice starch aggregates possess a high capacity for 2AP retention in their structures.
Encapsulation of 2AP in rice starch aggregates by headspace analysis with and without gelatinization
Note: RRS means non-glutinous rice starch, GRS means glutinous rice starch, PLE means aqueous pandan leaf extract.
Storage stability of encapsulated products Aggregates prepared by spray drying were stored in a metalized PET bag at ambient temperature for 10 weeks. The change in 2AP concentration in the headspace during storage was monitored. The results demonstrated that 2AP could be entrapped within rice starch aggregate. Figure 4 shows the effect of storing 2AP in rice starch aggregates at 30 °C for 10 weeks. The results revealed that after 10 weeks' storage, both the non-glutinous and glutinous rice starch aggregates showed possible 2AP encapsulation against storage. A reduction in 2AP was observed in all the powder samples during storage. Apitanapong and Noomhorm (2003) also demonstrated that 2AP encapsulated in gum acacia-maltodextrin decreased by 30% after 35 days' storage. Our results confirmed that the reduction in 2AP after 10 weeks' (70 d) storage was in the 12–29% range in glutinous rice starch aggregates and in the 10–20% range in non-glutinous rice starch aggregates (Figure 4). Accordingly, the type of starch, glutinous or non-glutinous, obviously had less influence on the shelf stability of 2AP in long-term storage.
2AP retention in non-glutinous and glutinous rice starch aggregates stored for 10 weeks at 30 °C
Note: RRS means non-glutinous rice starch, GRS means glutinous rice starch, PLE means aqueous pandan leaf extract.
Rice starch aggregates had the ability to entrap the potent flavor compound 2AP, as well as color, from fresh pandan leaf extract. The amylose content of rice starch and the amount of natural flavor added to the aggregates significantly affected the properties of the aggregates, i.e., color, flowability, pasting properties, and initial 2AP content. Encapsulated 2AP rice starches may allow the release of 2AP by gelatinization. Aggregate formation may provide a longer shelf life for pandan leaf extracts and improve the processing of Southeast Asian foods.
Acknowledgments This work was financially supported by the Kasetsart University Research and Development Institute (KURDI), Thailand, and the framework of an international collaborative research project entitled: “Establishment of food value chain through value-addition of local food resources for sustainable rural development”, supported by the Japan International Research Center for Agricultural Sciences (JIRCAS).
