Nghiên cứu ảnh hưởng của quá trình gia nhiệt ohm và tồn trữ đến các thành phần hóa lý của nước ép thanh long ruột đỏ

BỘ CÔNG THƯƠNG ĐẠI HỌC CÔNG NGHIỆP THÀNH PHỐ HỒ CHÍ MINH BÁO CÁO TỔNG KẾT ĐỀ TÀI KHOA HỌC KẾT QUẢ THỰC HIỆN ĐỀ TÀI NGHIÊN CỨU KHOA HỌC CẤP TRƯỜNG Tên đề tài: Nghiên cứu ảnh hưởng trình gia nhiệt Ohm tồn trữ đến thành phần hóa lý nước ép long ruột đỏ Mã số đề tài: 21.2CNHH07 Chủ nhiệm đề tài: TS Đồn Như Kh Đơn vị thực hiện: Viện Cơng nghệ Sinh học Thực phẩm Tp Hồ Chí Minh, ngày 01 tháng 08 năm 2023 Tp Hồ Chí Minh, … LỜI CÁM ƠN Trong trình thực đề tài “Nghiên cứu ảnh hưởng trình gia nhiệt Ohm tồn trữ đến thành phần hóa lý nước ép long ruột đỏ”, nhận tài trợ kinh phí nghiên cứu nhà trường, giúp đỡ trang thiết bị Viện Công Nghệ Sinh Học Thực Phẩm, chia sẻ kinh nghiệm đồng nghiệp, hướng dẫn thủ tục giấy tờ cán bộ, nhân viên phòng ban để hồn thành đề tài Tơi xin cảm ơn Ban giám hiệu, phòng Quản lý Khoa Học Hợp tác Quốc Tế, Viện Công Nghệ Sinh Học Thực Phẩm trường Đại Học Cơng Nghiệp, Tp Hồ Chí Minh hỗ trợ giúp đỡ tơi hồn thành nghiên cứu Mặc dù tơi nổ lực suốt q trình thực đề tài, song cịn có mặt hạn chế, thiếu sót Tơi mong nhận ý kiến đóng góp q thầy cơ, bạn độc giả PHẦN I THƠNG TIN CHUNG I Thơng tin tổng quát 1.1 Tên đề tài: Nghiên cứu ảnh hưởng trình gia nhiệt Ohm tồn trữ đến thành phần hóa lý nước ép long ruột đỏ 1.2 Mã số: 21.2 CNHH07 1.3 Danh sách chủ trì, thành viên tham gia thực đề tài Họ tên TT Đơn vị cơng tác Vai trị thực đề tài Viện Công Nghệ Sinh Học Chủ nhiệm đề tài (học hàm, học vị) TS Đoàn Như Khuê Thực Phẩm, Đại học Công Nghiệp, Tp Hồ Chí Minh TS Lê Nhất Tâm Viện Cơng Nghệ Sinh Học Thành viên Thực Phẩm, Đại học Cơng Nghiệp, Tp.Hồ Chí Minh ThS Nguyễn Thị Hương Viện Cơng Nghệ Sinh Học Thành viên Thực Phẩm, Đại học Cơng Nghiệp, Tp Hồ Chí Minh 1.4 Đơn vị chủ trì: Viện Cơng nghệ Sinh học Thực phẩm, Trường Đại học Cơng nghiệp Tp Hồ Chí Minh 1.5 Thời gian thực hiện: 1.5.1 Theo hợp đồng: từ tháng 03 năm 2022 đến tháng 03 năm 2023 1.5.2 Gia hạn (nếu có): từ tháng 03 đến tháng 09 năm 2023 1.5.3 Thực thực tế: từ tháng 03 năm 2022 đến tháng 07 năm 2023 1.6 Những thay đổi so với thuyết minh ban đầu (nếu có): Không thay đổi nội dung so với thuyết minh ban đầu (Về mục tiêu, nội dung, phương pháp, kết nghiên cứu tổ chức thực hiện; Nguyên nhân; Ý kiến Cơ quan quản lý) 1.7 Tổng kinh phí phê duyệt đề tài: 50 triệu đồng II Kết nghiên cứu Đặt vấn đề Thanh long loại trái trồng nhiều tỉnh thành, chủ yếu tỉnh Bình Thuận, Long An, Tiền Giang…với sản lượng lớn, thu hoạch quanh năm Phần lớn sản lượng long dùng tươi, bán nước xuất Do đó, lượng lớn long bị hư hỏng không sử dụng kịp thời Đồng thời, năm gần đây, nhu cầu thị trường xuất không ổn định làm cho long thường xuyên bị rớt giá Do đó, đa dạng hóa sản phẩm từ long để kéo dài hạn sử dụng nâng cao giá trị long sản phẩm chế biến từ long yêu cầu cấp thiết Theo số liệu thống kê, nhu cầu sử dụng nước ép trái Việt Nam giới lớn ngày tăng Nước ép long ruột đỏ (RFDFJ) giàu hợp chất có hoạt tính sinh học, đặc biệt betacyanin, hợp chất tạo nên màu đỏ tím tự nhiên có nhiều ứng dụng tiềm ngành cơng nghiệp thực phẩm Tuy nhiên, nước ép dễ bị hư hỏng nhiễm vi sinh vật (VSV) gây bệnh làm cho nước ép tính an tồn sử dụng, nhiễm VSV enzyme pectin methylesterase gây hư hỏng làm cho nước ép bị biến đổi màu sắc, cấu trúc, hương vị Các phương pháp gia nhiệt thông thường bất hoạt đối tượng gây bệnh gây hư hỏng dễ bị phân hủy chất dinh dưỡng, hợp chất có hoạt tính sinh học nhạy nhiệt betacyanin, hợp chất phenolic tổng, …và làm biến màu nước ép Gia nhiệt Ohm (OH) sinh nhiệt trực tiếp bên khối thực phẩm cho dòng điện chạy qua Nhiệt tạo đồng nhanh chóng tồn khối thực phẩm, ảnh hưởng đến thành phần nhạy nhiệt Ngoài ra, ảnh hưởng OH đến VSV tác động kép nhiệt điện, làm tăng hiệu vô hoạt VSV đồng thời hạn chế biến đổi chất lượng dinh dưỡng cảm quan nước ép Trong trình bảo quản xảy phản ứng oxy hóa, làm cho số hợp chất hóa học đặc trưng nước ép bị phân hủy, đó, bổ sung axit ascorbic hạn chế phân hủy hợp chất Hiện chưa có số liệu nghiên cứu ảnh hưởng OH đến thành phần có hoạt tính sinh học màu sắc nước long ruột đỏ (RFDFJ) Do đó, chúng tơi nghiên cứu tác động OH thời gian bảo quản thành phần có hoạt tính sinh học màu sắc RFDFJ, đồng thời theo dõi tác động bổ sung chất chống oxy hóa đến chất lượng nước ép trùng phương pháp gia nhiệt Ohm Mục tiêu a) Mục tiêu tổng quát: Nghiên cứu phương pháp gia nhiệt Ohm, thay cho phương pháp gia nhiệt thông thường để xử lý nước ép long ruột đỏ nhằm tạo sản phẩm nước ép chế biến có chất lượng cao b) Mục tiêu cụ thể - Đánh giá tác động phương pháp trùng nhiệt thông thường trùng phương pháp gia nhiệt Ohm đến hợp chất hóa học khả chống oxy hóa nước ép long ruột đỏ - Đánh giá độ ổn định khả chống oxy hóa thành phần hóa học nước ép long ruột đỏ trùng phương pháp gia nhiệt Ohm suốt trình tồn trữ - Đánh giá hiệu bổ sung axit ascorbic đến hợp chất hóa học hoạt tính chống oxy hóa nước ép long ruột đỏ trùng phương pháp gia nhiệt Ohm suốt trình tồn trữ Phương pháp nghiên cứu Để trùng nước ép long, cần xác định chế độ xử lý bất hoạt VSV enzyme gây hư hỏng Một số thí nghiệm sơ thực để xác định chế độ trùng bất hoạt hoàn toàn vi sinh vật khoảng 90% enzyme gây tách lớp nước ép, pectin methylesterase (PME) Chế độ trùng Ohm áp dụng nghiên cứu gia nhiệt từ 20 đến 85 °C (51s) giữ 85 °C 60 s - Khảo sát biến đổi betacyanin, phenolic tổng, DPPH, màu sắc nước ép long ruột đỏ sau xử lý nhiệt Ohm xử lý nhiệt thông thường theo dõi tuần + Gia nhiệt Ohm: Lấy 50ml nước ép long ruột đỏ, gia nhiệt Ohm (OH) từ 20 đến 85 °C giữ nhiệt 85 °C 60 s, điều kiện xử lý nhiệt OH tần số 60 Hz cường độ điện trường 30 V/cm Sau đạt nhiệt độ thời gian xử lý, mẫu làm lạnh nhanh nước đá (0oC) Sau đó, cho vào chai tối tồn trữ lạnh (4 oC) Sau 0, 1, 2, 3, 4, 5, 6, 7, tuần bảo quản, lấy mẫu để đo tiêu cần khảo sát + Gia nhiệt thường (CH): Rót 50 mL nước ép bưởi cho vào hộp inox có kích thước với buồng gia nhiệt Ohm đặt bể ổn nhiệt (Memmert WNB14, Germany) với nhiệt độ nước bể 95oC Gia nhiệt nước ép từ 20 đến 85 °C 300s giữ 85 °C 60 s Sau đạt nhiệt độ thời gian xử lý, mẫu làm lạnh nhanh nước đá (0oC) Sau đó, cho vào chai tối tồn trữ lạnh (4oC) Sau 0, 1, 2, 3, 4, 5, 6, 7, tuần bảo quản, lấy mẫu để đo tiêu cần khảo sát Mẫu nước ép long sau xử lý nhiệt phương pháp OH CH bảo quản 4oC chai tối Các tiêu pH, hàm lượng betacyanin, hàm lượng phenolic tổng, hoạt tính chống oxy hóa màu sắc theo dõi phân tích trước sau xử lý nhiệt, sau tuần bảo quản suốt tuần - Ảnh hưởng việc bổ sung axit ascorbic để ổn định hàm lượng betacyanin, hàm lượng phenolic tổng, DPPH, màu sắc nước ép long ruột đỏ suốt thời gian tồn trữ Lấy 50ml nước ép long ruột đỏ, xử lý OH/CH Sau đạt nhiệt độ 80 oC giữ nhiệt 60 s, mẫu làm lạnh nhanh nước đá (0oC) Hút 10 mL nước ép cho vào chai tối bổ sung axit ascorbic để đạt nồng độ 0,25 % tồn trữ lạnh (4oC) Mẫu không bổ sung axit ascorbic chuẩn bị làm mẫu đối chứng Sau 0, 1, 2, 3, 4, 5, 6, 7, tuần bảo quản, lấy mẫu để đo tiêu cần khảo sát (hàm lượng betacyanin, hàm lượng phenolic tổng, hoạt tính chống oxy hóa màu sắc) Tổng kết kết nghiên cứu 4.1 Sự biến đổi tính chất hóa lý hàm lượng số thành phần có hoạt tính sinh học nước ép long sau xử lý nhiệt Ohm xử lý nhiệt thông thường Hàm lượng chất khơ hịa tan (TSS), pH, màu sắc nước ép xử lý hai phương pháp khơng khác biệt có ý nghĩa thống kê, không khác so với mẫu tươi Kết phương pháp gia nhiệt CH OH không ảnh hưởng đến TSS, pH, màu sắc nước ép gia nhiệt (p>0,05) Phương pháp gia nhiệt OH, CH tác động khác đến biến đổi hàm lượng phenolic tổng (TPC) DPPH nước ép long ruột đỏ không ảnh hưởng đến hàm lượng betacyanin (BC) chế độ xử lý CH OH 85 oC 60 s Nước ép gia nhiệt OH có TPC DPPH tương tự mẫu tươi (p>0,05), mẫu nước ép CH bị phân hủy TPC DPPH (p0,05) Sau đó, hàm lượng betacyanin giảm dần tuần tiếp theo, giảm mạnh từ tuần thứ 6, giảm 32 % so với tuần (p 0.98) A comparison of the OH process with conventional heating (CH) showed that OH resulted in less degradation to BC, TPC and antioxidant activity than CH OH is a suitable technology for processing red-fleshed dragon fruit juice Adding 0.25% AA to the juice helped reduce changes in colour, BC, TPC and antioxidant activity (P < 0.05) Keywords Ascorbic acid, betacyanin, colour, Ohm heating, red-fleshed dragon fruit juice, storage Introduction Red-fleshed dragon fruit is a tropical fruit native to Central and South America but is now commonly grown in Southeast Asia, especially in Vietnam Most of this dragon fruit production is used as fresh fruit for domestic sale or export There is often a large amount of damage due to not using it in time In recent years, the damage rate of dragon fruit has increased when it cannot be exported due to the Covid epidemic Therefore, diversifying processed products is a very necessary need as the demand for fruit juice in the world is very large and growing By 2023, the revenue of juice segment will reach USD 116.80 billion and is estimated to grow at 3.65% (2023–2027) (https://www.statista.com/outlook/cmo/non-alcoholicdrinks/juices/worldwide) Red-fleshed dragon fruit juice (RFDFJ) is rich in biologically active compounds, particularly betacyanin *Correspondent: E-mail: doannhukhue@iuh.edu.vn doi:10.1111/ijfs.16483 Ó 2023 Institute of Food, Science and Technology (IFSTTF) (BC) (Le, 2022), responsible for the fruit’s natural colour and potential applications in the food industry (Lin et al., 2022) There are many studies applying conventional heating methods to processing dragon fruit juice However, BC is sensitive to heat, easily degraded and can turn from red to brown, a colour that consumers not accept (Wong & Siow, 2015) Herbach et al (2007) emphasised that the using of minimum heat method resulted in stabilising the BC in the red-fleshed dragon puree after pasteurisation Currently, there are many advanced techniques for pasteurising/sterilising food that help food achieve microbiological safety while limiting changes that reduce the quality of food, such as Ohmic heating (OH) (Doan et al (2021a, 2021b)), microwave (Igual et al., 2010), radio-frequency heating (Awuah et al., 2014) Among them, OH is a promising electrical heating technique for liquid food, including high viscosity food (McKenna et al., 2006) OH generates direct heat inside the food product when a current goes through the food mass, with the food acting as a Ohmic heating and ascorbic acid to juice D N Khue et al resistor (Dealwis & Fryer, 1992) Heat is generated uniformly and quickly, and thus, it has little effect on heat-sensitive components (De Halleux et al., 2005; Mercali et al., 2014a) In addition, the influence of OH on microorganisms is dual, in addition to the effect of heat, there is also the effect of electricity, which increases the effectiveness of microorganism inactivation (Khue et al., 2020) Therefore, the temperature required to inactivate microorganisms is lower than that of conventional heating, also contributing to protecting biologically active compounds, heat-sensitive components in fruit juice (Doan et al., 2021a, 2021b) Therefore, applying ohmic pasteurisation to dragon fruit juice may be suitable to preserve biologically active compounds and prolong the shelf life of the juice Moreover, some previous studies have also shown that adding ascorbic acid (AA) (0.25%) to the juice can limit the degradation of BC and bioactive components (Khan & Giridhar, 2014) (Wong & Siow, 2015) Currently, there are no research data on the effects of OH on bioactive components and colour of dragon fruit juice Therefore, we investigated the effects of OH and storage time on bioactive components and colour of RFDFJ, while also monitoring the impact of adding antioxidant to the Ohm-heated juice during the storage period to evaluate the quality change of the juice Materials and methods Chemicals Gallic acid, ascorbic acid standards and DPPH were manufactured by Sigma-Aldrich Folin–Ciocalteu reagent was obtained from Merck Vietnam Ltd Co All chemicals and reagents were analytical grade Red-fleshed dragon juice preparation Red-fleshed dragon fruits (Hylocereus polyrhizus) were collected from farm in Vinh Long, Vietnam and were transferred to the laboratory 24 h after harvesting The fruits were ripe, evenly coloured and not bruised or damaged, with a weight of 0.4  0.05 kg The fruits were peeled, and then squeezed with a juicer The juice was filtered through sterilised double-layered cloth The juice was then well mixed to obtain uniformity and poured into dark glass bottles All samples were stored at
18 °C to reduce the rate of reactions until further use Samples of dragon fruit juice after OH and conventional heating (CH) were stored in the dark in bottles at °C pH, betacyanin content (BC), total phenolic content (TPC), antioxidant activity and colour were monitored and analysed every week for weeks International Journal of Food Science and Technology 2023 Ohmic heating apparatus The Ohm heater consisted of a heating chamber, a function generator, a power amplifier and a data logger The heating chamber had two titanium electrodes with a distance of cm between the two electrodes A schematic diagram of the OH apparatus was shown in our previous study (Khue et al., 2020) Frequency of 60 Hz and electric field strength of 30 V cm
1 were installed The temperature was monitored with a digital temperature probe positioned at the centre of the chamber to collect data Heating treatments To pasteurise RFDFJ, it is necessary to determine the inactivation conditions of bacteria causing spoilage For the OH treatment, 50 mL of RFDFJ was poured into the heating chamber and heated from 20 to 85 °C (for 51 s), and maintained at 85 °C for 60 s to fully inactivate microorganisms For the conventional heating treatment (CH), 50 mL of RFDFJ was poured into an inox chamber (the same size as the ohm heating chamber) and placed in a thermostatic water bath (Memmert WNB14, Germany) operating at 95°C The juice took 300 s to reach 85 °C and was then maintained at this temperature for 60 s After the treatment, the samples were stored in dark bottles at °C Samples were taken at 0, 1, 2, 3, 4, 5, 6, and weeks for analysis, and all runs were done in triplicate The effect of adding ascorbic acid on the bioactive compounds and colour of RFDFJ after OH for weeks were also studied and compared with CH samples Ascorbic acid was added to the pasteurised juice samples (OH and CH) at °C to obtain a content of 0.25% (w/v) A sample without the addition of ascorbic acid was used as a control The treated juice was stored in dark bottles with a capacity of 10 mL and placed in a refrigerator at °C The betacyanin, polyphenol, and DPPH content of each treated sample were assessed during storage time Analytical methods • pH was measured using a digital pH metre (Mettler FE20, Mettler Toledo, China) as described by Doan et al (2021b) • Total soluble solids (TSS) were measured as described by Doan et al ( 2021b) • The betacyanin content (BC) in RFDFJ was determined by spectrophotometry according to the method of Siow & Wong (2017) 0.1 mL of the sample was diluted with 3.9 mL of McIlvaine buffer (pH 6.5), Ó 2023 Institute of Food, Science and Technology (IFSTTF) Ohmic heating and ascorbic acid to juice D N Khue et al and the absorption was measured at 537 nm The BC was calculated based on the weight of betanin (Bc) according to the formula (1)
mg A  F  MW  1000 (1) ¼ L εl where A is the absorption value at 537 nm, F is the dilution factor, MW is the molecular weight of betanin (550 g mol
1), ε is the molar extinction coefficient of betanin (60 000 L mol
1 cm
1) and l is the length of the cuvette (1 cm) BC • Total phenolic content (TPC) was determined as described by Doan et al ( 2021b) 0.1 mL of centrifuged juice was added to mL of the Folin–Ciocalteu reagent (10%) Then mL of sodium carbonate (75 g L
1) was added The mixture was incubated in the dark at 30 °C for 60 The absorbance was measured at 765 nm by a spectrophotometer (Thermo Spectronic Genesys 20, USA) Gallic acid was used as a standard phenolic with a standard curve range of 0–400 mg L
1 of gallic acid The amount of TPC was expressed as mg of gallic acid equivalent (GAE) per 100 mL of juice • DPPH free radical scavenging activity (antioxidant capacity) was assessed as described by S´anchezMoreno et al (2003) 0.1 mL of the centrifuged juice/ deionised water was added to 3.9 mL of DPPH (0.03 g L
1 in methanol) Following 60 incubation at 30 °C in the dark, absorbance was measured at 515 nm Antioxidant capacity of the juice was expressed as % DPPH inhibition using the formula (2)  Acontrol
Asample %DPPH ¼ Acontrol  (2) where Acontrol is the absorbance of deionised water in solution (DPPH 0.03 g L
1) and Asample is the absorbance of the fruit juice in solution (DPPH 0.03 g L
1) Colour analysis The colour of the fruit juice was measured using a Minolta colourimeter (CR400 Chroma, Minolta, Tokyo, Japan) following the method of Vikram et al (2005) The juice was poured into a quartz cuvette up to the mark, then placed into the colorimetric accessory for liquids The results were displayed in the L*, a* and b* colour spaces The colour difference between the test sample and control (fresh juice) was calculated using the value of ΔE, which was calculated using the formula (3): q (3) E ẳ a
a0 ị2 ỵ b
b0 ị2 ỵ L
L0 ị2 ể 2023 Institute of Food, Science and Technology (IFSTTF) where L*, a* and b* are the measured values of the test sample, and L0*, a0* and b0* are the measured values of the control sample used for comparison Statistical analysis All tests were performed in triplicate and data were shown as mean  standard deviation Statistical analysis was done using Statgraphics Centurion XV software (Statgraphics Technologies, Inc., Virginia, USA) The significant difference in mean values was assessed to one-way analysis of variance (ANOVA) and the difference between the treatments was tested for LSD with the significance level of P < 0.05 Results Changes in physicochemical properties and content of some bioactive components in dragon fruit juice after heat treatment The changes in physical properties and bioactive components of RFDFJ treated with OH were compared to the juice treated with CH as shown in Table The TSS, pH and colour of the processed juice using both methods were not significantly different and were also not different from the fresh sample (Table 1) These results indicate that OH and CH not affect TSS, pH and colour of the juice when heated at 85 °C and held for 60 s (P > 0.05) Park et al (2017) showed treated apple juice with OH retained the same colour as the fresh sample The colour of pineapple juice and orange juice treated with OH was not different from those treated with CH with the same heating rate (Tumpanuvatr & Jittanit, 2012) Makroo et al (2017a) showed that TSS in watermelon juice did not change after being heat treated with CH and OH Igual et al (2010) reported that TSS was not affected by temperature and holding time when heating grapefruit juice at 80 °C for 80 s and keeping it at that temperature for 11 s Similarly, pH also did not change during the heat treatment process of pomelo juice from 20 to 80 °C (Doan et al., 2021b) However, Darvishi et al (2020) reported that the pH of grape juice changed after being heat treated from 19 to 90 °C, and the change in pH during CH for 73 was greater than that during OH for 10 In contrast, some authors have also observed an increase in pH of watermelon juice (Makroo et al (2017a, 2017b)) and sour cherry juice (Norouzi et al., 2021) after being treated with OH compared to CH The increase in pH after OH treatment may be due to electrolysis or electrochemical interactions (Makroo et al., 2017a) However, because the OH rate was high, the sample heating time was reduced, resulting in limited changes in pH due to the decreased reaction time (Darvishi et al., 2013) International Journal of Food Science and Technology 2023 Ohmic heating and ascorbic acid to juice D N Khue et al Table Brix, pH, total polyphenol content, betacyanin content, antioxidant activity and colour in fresh juice (FJ), conventional heating (CH) and ohmic heating (OH) juice FJ TSS (Bx) pH TPC (mg/100 mL) BC (mg/100 mL) DPPH (%) L* a* b* 14.2 5.35 33.08 33.88 81.75 71.07 49.39 17.31 OH a (0.21) (0.06)a (0.30)a (0.11)a (0.84)a (0.07)a (0.24)a (0.09)a 14.3 5.29 32.62 33.12 81.51 71.13 49.42 17.35 that determines the colour of the juice The BC did not degrade after heat treatment (P > 0.05), so the colour of the juice remained unchanged (Table 1) CH a (0.38) (0.07)a (0.28)a (0.60)a (0.48)a (0.13)a (0.17)a (0.08)a 14.1 5.20 29.00 33.65 75.2 71.26 49.61 17.19 (0.09)a (0.06)a (0.69)b (0.66)a (0.72)b (0.23)a (0.17)a (0.35)a Values reported as mean  SD, values were run in triplicates The letters a and b on the same row represent significant differences (P < 0.05) Therefore, changes in acidity, TSS and colour depend on the treatment temperature and time, heating rate and juice composition The OH/CH have different effects on the changes in TPC and DPPH in RFDFJ but not affect BC (Table 1) Betalains belong to the TPC group, which are biologically active compounds (Herbach et al., 2007) Betalains consist of betacyanin (red–purple) and betaxanthin (yellow) However, only betacyanin is present in RFDF (Wong & Siow, 2015) In this study, betacyanin was not degraded under CH and OH treatment at 85°C for 60 s (Table 1) Wong & Siow (2015) suggested that holding time below 30 did not significantly affect the BC in dragon fruit juice when treated at a temperature lower than 80 °C Similarly, Trang et al (2020) showed no difference in BC in fruit extract when heating from 65 to 80 °C for 30 min, but BC began to decrease significantly at 85– 95 °C The remaining BC after heating at 85 °C for was 73.65% The OH-treated juice had TPC and DPPH similar to fresh samples (P > 0.05), while the CH-treated juice showed degraded TPC and DPPH (P < 0.05) Heat-sensitive compounds such as TPC and antioxidant activity in CH-treated juice decreased by 9.6% and 8.1% compared to untreated samples respectively This result may be due to the fact that with the same volume of pasteurised juice (50 mL), the CH rate was usually six times longer than the OH rate, which was 304 and 51 s to reach 85 °C respectively Prolonged processing time in CH caused oxidative reactions that degraded heat-sensitive compounds (Mercali et al., 2014b; Doan et al., 2021a, 2021b) Some studies suggested that the red colour of RFDFJ was mainly due to the presence of betacyanin, with possibly a small amount of anthocyanin (Herbach et al., 2007) In our preliminary experiment, we found no significant amount of anthocyanin in the juice sample Therefore, betacyanin was the main component International Journal of Food Science and Technology 2023 Effect of storage time on betacyanin content with ohmic and conventional heating The changes in BC in RFDFJ treated with OH and CH and stored for weeks are shown in Fig The OH-treated juice did not degrade BC and remained stable for week with 33.22 mg/100 g (P > 0.05) Subsequently, the BC gradually decreased over the following weeks, and sharply decreased from the 6th week to 23.00  0.51 mg/100 mL, a decrease of 32% compared to week (P < 0.05) After weeks, BC was 17.56  0.28 mg/100 g, a decrease of approximately 48% Betacyanin in CH-treated juice also showed a similar trend of changes to that in OH-treated juice However, the BC in CH-treated juice was degraded more from the 3rd week (P < 0.05) The retention rate of BC in CH-treated juice after weeks was 75.54% at °C, similar to the study by Lin et al (2022) Herbach et al (2007) reported the thermal degradation of BC in the pH range of 3.0–7.0, following first-order degradation kinetics The storage process involved oxidation, which affected the stability of BC (Tang & Norziah, 2010) The stability of betanin pigment increased four to five times when oxygen was removed (Huang & Elbe, 1987) Effect of storage on total phenolic content treated with ohmic and conventional heating The TPC of the red dragon fruit juice after weeks is shown in Fig The initial TPC in the juice after OH (week 0) was 32.62  0.28 mg/100 mL, which was not significantly different from the fresh sample This Betacyanin (mg/100 mL) 40 30 20 10 0 Storage time (week) Figure Changes in BC after OH and CH and storage (adding AA: ○-CH-0%; ●-OH-0%; Δ-CH-0.25%; ▲-OH-0.25%) Ó 2023 Institute of Food, Science and Technology (IFSTTF) 40 100 80 30 %DPPH TPC content (mg/100 mL) Ohmic heating and ascorbic acid to juice D N Khue et al 20 10 60 40 20 0 Storage time (week) Figure Changes in TPC after OH and CH and storage (adding AA: ○-CH-0%; ●-OH-0%; Δ-CH-0.25%; ▲-OH-0.25%) result was similar to the study by Abd Manan et al (2019) who determined the TPC in RFDFJ was 32.90  0.92 mg/100 mL However, TPC gradually decreased during the subsequent weeks, with the TPC in ohmic-treated juice decreasing to 27.62 mg/100 mL —reduction by 16.45% after weeks, 38.63% after weeks and 60.58% after weeks (P < 0.05) The TPC in CH-treated juice also decreased but at a faster rate than that of OH, decreasing by 35.23% after days, 63.2% after days and 65.49% after weeks The reduction in TPC may be due to the oxidation of some TPC or enzymatic reactions that cause polymerisation during storage (Cheynier, 2005) OH had a faster heating rate, resulting in less TPC degradation compared to the CH method BC is the main component of TPC in RFDFJ (Choi et al., 2002; Ramli et al., 2014) The decrease in BC during storage was consistent with the general trend observed in many studies, resulting in a decrease in TPC (Wilkes et al., 2014; Wojdyøo et al., 2014) Effect of storage time on antioxidant activity (DPPH) treated with ohmic and conventional heating The antioxidant activity of RFDFJ after weeks is shown in Fig The percentage inhibition of DPPH in stored juice at °C was stable for week However, it gradually decreases over time For OH, after weeks, inhibition of DPPH decreased from 81.51  0.89% to 49.60  1.34% (P < 0.05) For CH, inhibition of DPPH in the juice samples was lower (3.63%–10.75%) than in the OH samples (P < 0.05) Phenolics play an important role in antioxidant activity, removing free radicals in the juice through hydrolysis or electron donation With an increase in storage time, TPC decreased, primarily due to a decrease in BC, resulting in a decrease in the antioxidant activity of dragon fruit juice These results are Ó 2023 Institute of Food, Science and Technology (IFSTTF) Storage time (week) Figure Changes in DPPH after OH and CH and storage (adding AA: ○-CH-0%; ●-OH-0%; Δ-CH-0.25%; ▲-OH-0.25%) similar to those of Lin et al (2022) who investigated the antioxidant activity of red dragon fruit juice during 21 days of storage Colour change (ΔE) in red-fleshed dragon fruit juice after ohmic and conventional heating Colour plays an important role in enhancing the sensory value of food products However, some components that create colour are lost during heat processing and storage, or due to the formation of brown pigments resulting from the reaction between amino acids and reducing sugars (Maillard reaction) or the degradation of gas and ascorbic acid, combined with reactions of carbonyl compounds to create brown colour (Choi et al., 2002) This colour change reduces the sensory and nutritional quality of the product Changes in the colour of the samples were evaluated using the colour difference (ΔE) calculated through the L*, a* and b* values of processed and stored samples for weeks 0–8 compared to fresh samples (Fig 4) The results show no difference between the OH sample (week 0) and the fresh sample (P > 0.05) Colour stability is maintained after heating and during week of storage, then gradually fades over time The ΔE value indicates that the colour change of OH-treated juice cannot be perceived by the eye (▵E < 3) for weeks of storage and that of CH is weeks After weeks of storage, the OH-treated sample has ΔE = 8.00 The colour of CH-heated juice fades faster than that of OH-treated juice (ΔE = 9.12) To determine the effect of BC on the colour of the juice, the correlation between the variation in BC and colour change during weeks was determined The results showed a correlation between the variation in BC and colour change of the juice (correlation coefficient: r = 0.989 and 0.987, respectively OH and CH) The regression equation for these two correlation factors is shown in Table International Journal of Food Science and Technology 2023 Ohmic heating and ascorbic acid to juice D N Khue et al 10 ∆E 6 0 Time (Week) sample also decreased over time, and the remaining BC was lower than that of the OH sample After weeks, it decreased by nearly 13%, and after weeks, it decreased by 33% In addition to AA, some previous studies have also shown that BC in dragon juice, as well as in solutions containing pure BC pigments, are more stable when supplemented with compounds such as isoascorbic, citric acid or a mixture of ascorbic acid and Se4+ (Khan & Giridhar, 2014) Therefore, future studies may consider supplementing a mixture of antioxidant compounds when storing RFDFJ treated with OH to assess juice quality Figure Changes in colour after OH and CH (○-CH; ●-OH) The effect of adding ascorbic acid on the total polyphenol and DPPH content of red-fleshed dragon juice Table Linear regression equation between betacyanin content variation and colour change during week OH samples CH samples E ẳ
5:0217BC ỵ 1:3184 R2 = 0.9802 Week to week E ẳ
7:8911BC ỵ 12:367 R2 = 0.9612 Week to week ΔE ¼
4:0508ΔBC R2 = 0.8558 Week to week ΔE ¼
7:1112ΔBC þ 11:835 R2 = 0.9585 Week to week The results indicate that there was a close correlation between the changes in betacyanin and colour of dragon fruit juice, similar to previous studies (Herbach et al., 2007) Therefore, if treatment condition could be taken to stabilise the BC in the juice, the colour of RFDFJ could also be stabilised BC and other bioactive compounds were degraded during storage due to oxidation Therefore, adding ascorbic acid (AA), an antioxidant, could increase the stability of BC, TPC, DPPH and the colour of the juice (Wong & Siow, 2015) AA enhanced the stability of BC by removing oxygen from the surrounding environment since oxygen was a factor that increases the rate of BC degradation (Ernest & Joachim, 1982) According to the results of many studies, supplementing with 0.25% AA maintained the highest stability of BC (Wong & Siow, 2015) This study investigated the effect of adding 0.25% AA on the stability of BC in heated juice (OH and CH) during weeks, as shown in Fig The addition of AA improved the stability of BC in the juice For the OH-heated juice sample, the BC in the sample with 0.25% AA did not differ from the untreated sample after weeks of storage (P > 0.05), but gradually decreased over the following weeks After weeks, it decreased by about 6%, and decreased significantly in the 5th week (decreased by 16%) After weeks, it decreased by 30% Similarly, BC in the CH-heated International Journal of Food Science and Technology 2023 Ohmic-heated and AA-supplemented samples had the slowest TPC degradation during storage (Fig 3) After weeks, TPC in the OH sample with 0.25% added AA decreased by nearly 50%, while the sample without added AA decreased by over 60% Similarly, in CH samples, the TPC degradation was slower in the AA-supplemented samples during storage Figure showed the OH samples with 0.25% AA had the highest and most stable antioxidant activity, which was 12% higher than the fresh sample This result was also consistent with the study of Murakami et al (2003) These authors added AA to phenolic compounds and identified increased antioxidant activity The antioxidant activity of the juice decreased slowly over time, with DPPH above 80% for the OH juice (a decrease by 10.89% after weeks) Therefore, RFDFJ with added AA protects BC and TPC, which are antioxidant components in the juice Conclusions Red-fleshed dragon fruit juice is a promising source of antioxidants and natural colour compounds OH retained higher levels of TPC, BC, antioxidant activity and colour of the juice than CH The colour changes in the juice were closely related to changes in BC Adding 0.25% AA to the juice reduced the degradation of BC and TPC, and stabilised the antioxidant activity OH is a promising technology for processing RFDFJ, and adding AA to the juice can help maintain the nutritional and sensory qualities of the juice To apply these techniques in the food industry, further studies are needed to investigate continuous and pilotscale fruit juice processing Acknowledgments We acknowledge the Industrial University of Ho Chi Minh City funded for the research ‘The effect of Ohm Ó 2023 Institute of Food, Science and Technology (IFSTTF) Ohmic heating and ascorbic acid to juice D N Khue et al heating and storage on physico-chemical components of red fleshed dragon fruit juice’ [grant number 21.2CNHH07-24/3/2022] Author contributions Khue Nhu Doan: Conceptualization (lead); data curation (lead); formal analysis (lead); methodology (lead); project administration (lead); validation (lead); writing – original draft (lead); writing – review and editing (lead) Huong Thi Nguyen: Methodology (supporting); supervision (equal) Tam Nhat Le: Methodology (equal) Uyen Thuy Xuan Phan: Data curation (equal); software (equal) Minh Tuan Minh Pham: Methodology (equal); supervision (equal) Dat Quoc Lai: Conceptualization (supporting) Phung T.Kim Le: Conceptualization (supporting) Conflict of interest The authors declare that they 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(Hylocereus polyrhizus) juice and concentrate as models Journal of Food Science and Technology, 52, 3086–3092 Supporting Information Additional Supporting Information may be found in the online version of this article: Data S1 Data of betacyanin changes, total phenolic content, antioxidant activity, colour of red-fleshed dragon fruit juice after ohmic heating and ascorbic acid addition during storage Ó 2023 Institute of Food, Science and Technology (IFSTTF)