Báo cáo Nghiên cứu khoa học Maintaining fruit quality and increasing shelf life of pomelo in the mekong delta of southern Vietnam

1 CARD PROJECT 050/04 VIE Improvement of export and domestic markets for Vietnamese fruit through improved post-harvest and supply chain management MAINTAINING FRUIT QUALITY AND INCREASING SHELF LIFE OF POMELO IN THE MEKONG DELTA OF SOUTHERN VIETNAM By Robert Nissen1, Nguyen Duy Duc2, Ms San Tram Anh2, Ms Tran Thi Kim Oanh2, Mr Vu Cong Khanh2 & Mr Ngo Van Binh2, 1 Queensland Department of Primary Industries and Fisheries (DPI&F) , Maroochy Research Station, PO Box 5083 SCMC, Queensland, Australia, 4560. 2 Southern Sub-Institute of Agricultural Engineering and Post-Harvest Technology (SIAEP), 54 Tran Khanh Du Street, District 1, Ho Chi Minh City, Vietnam. 2 MAINTAINING FRUIT QUALITY AND INCREASING SHELF LIFE OF POMELO IN THE MEKONG DELTA OF SOUTHERN VIETNAM Robert Nissen1, Nguyen Duy Duc2, Ms San Tram Anh2, Ms Tran Thi Kim Oanh2, Mr Vu Cong Khanh2 & Mr Ngo Van Binh2, 1 Queensland Department of Primary Industries and Fisheries (DPI&F) , Maroochy Research Station, PO Box 5083 SCMC, Queensland, Australia, 4560. 2 Southern Sub-Institute of Agricultural Engineering and Post-Harvest Technology (SIAEP), 54 Tran Khanh Du Street, District 1, Ho Chi Minh City, Vietnam. INTRODUCTION In Southern Vietnam, traditional wet market supply chains for agricultural fresh food are now giving way to new supermarket-led supply chain systems. The rapid transformation in the fruit and vegetables sector is due to the meteoric rise of supermarkets, hypermarkets, superstores, neighborhood stores, convenience stores, discount stores in Southern Vietnam. This change is impacting on both the upstream and downstream agricultural food supply chain participants through demands for safe, high quality and sustainable-produced fresh products and the greatest impact is being felt by the small farmers of southern Vietnam. Problems with traditional procurement supply chain practices include low- or no product standards, supply inconsistencies, highly variable transaction costs and limited or sequestered market information. Supermarkets are now setting new procurement practices and supply systems which focus on reducing costs and improving quality to enable them to sell at lower prices. This will allow them to win over consumers and obtain a larger share of their target market. The ability of many small farmers, collectors and wholesalers in the Mekong Delta of Vietnam to meet safe food levels and quality demands of domestic and overseas supermarkets can only be obtained through investing in improvements in their production and supply chain practices. Implementation of new production and post–harvest practices and the modernisation of these supply chains may prevent some small farmers from participating. Many small farmers will have to develop risk minimisation strategies, such as forming groups, implementing new crop management and production systems, improved packaging, more efficient transport methods and handling practices to provide a safe, competitively priced quality product. Understanding how to develop new supply chains and where to make changes is essential if farmers and all chain participants are to benefit. Many farmers are now realising that pomelo is a perishable fruit and traditional chains may have to change. Pomelo fruit suffer severely from moisture loss. Loading and unloading occurs at the local markets in the hot sun, speeding up the desiccating of the fruit. This moisture loss changes the fruit appearance, making the fruit less desirable, affecting its salability. High quality class fruit (extra or super class fruit and class 1 fruit) are often marketed with stalks attached. This is done to reassure customers that the fruit they are purchasing fresh produce. These stalks often break off during handling and transport and also draw moisture from the fruit. Farmers, collectors, traders, packaging agents and wholesalers estimates of fruit damage is from 1 to 2%, but surveys found that it is often above 10% due to moisture loss, handling damage and disease attack. 3 Therefore, this CARD Project set up experiments to evaluate the benefits of developing new post- harvest practices to improved fruit quality by reducing moisture loss for the pomelo supply chains operating in southern Vietnam. METHODOLOGY Because pomelo fruit suffer from the loss of moisture, this CARD project set up an experiment to reduce this moisture loss and increase shelf life and retail value of pomelo fruit. An anti-transparent and vacuumed wrapping of fruit in polyethylene bags were trialed to determine if this moisture loss could be significantly reduced. The pomelo variety “Nam Roi” was chosen as the variety on which to conduct the experiments. Nam Roi is famous pomelo variety in Vietnam as the fruit are sought after by many Vietnamese consumers. It has special fruit qualities such as:- • seedless • yellow flesh colour • the flesh is crisp and sweet TREATMENTS Fruit assessments were carried out at the SIAEP laboratory in Ho Chi Minh City. Treatments were applied to the pomelo fruit and fruit stored on the bench in the laboratory at SIAEP at about 25oC. Mature pomelo fruit purchased from the Thuy Duc Wholesale Markets in Ho Chi Minh City were used in this experiment. Experimental design consisted of three treatments of 10 fruit per rep sampled every 7 days for 12 weeks. Treatments applied were: 1. Control 2. Citra Shine Special Wax applied to the fruit • CITRASHINE is a shellac-based wax formulated with purified natural secretion and water-soluble emulsifying agents. It does not contain any solvents but water and all ingredients are approved for use on foodstuf by the Health regulations in most countries. This product is USFDA approved. • CITRASHINE is stable and anti-transparent and the long-lasting shine which it provides improves citrus fruit appearance and skin resistance, increasing the fruit market value. In addition CITRASHINE controls dehydratation and prevents fruit from excessive weight loss. Fruits were cleaned by detergent deccosol before apply the wax to remove dirt, dust and foreign material. 3. Vacuum sealed polyethylene plastic film applied to the fruit (wrapping) • A Lavezzini Vacuum Packaging Systems, Model Boxer was used to wrap and seal the pomelo fruit in a 0.014 mm Liner Low Density Polyethylene (LLDPE) plastic film. FRUIT MEASUREMENTS Assessments undertaken were: • Average fruit weight in grams and percentage moisture loss over time • Skin colour change over time using a Minolta Chromometer CR 200 and expressed as L a b values • Titrateable Acid measured using 10 grams of flesh in 100ml of double distilled water and macerated. This solution was then filtered through cotton wool and 10 mls of juice was collected and 2 drops of phenolphalayene indicator was added and titrated with Sodium Hydroxide (NaOH) 0.1 normal solution, until colour change occurred. 4 • Total soluble solids or degree Brix, was measured using a temperature compensation hand held Atago Refractometer Model N-1E. • Vitamin C content was measured using Association of Analytical Chemists (AOAC) International method 967.21. Procedure used was: o Take 10 g of fruit flesh and grind with 5 ml Metaphosphoric-acetic solution. o Remove all sample and place into a 100ml flask and add Metaphosphoric-acetic solution until it reaches 100mls and shake o Filter through absorbent cotton or rapid paper o Take 10ml of the above solution and place into a 100ml glass beaker o Titrate this solution with 2,6 diclorophenol indophenolat natri until fast pink colour appears. This takes about 2 minutes to occur o Count amount of 2,6 DCPIP need to titrate 1mg acid ascorbic ƒ + Take 2 ml standard acid ascorbic solution add 5 ml Metaphosphoric-acetic ƒ +Titrate with 2,6 diclorophenol indophenolat natri until fast pink colour appears in about 2 minutes (note number ml : y) o Titrate blank sample with 2,6 diclorophenol indophenolat natri until fast pink colour appears. This takes about 2 minutes to occur (note number ml = B) Calculation Content of Vitamin C = Pv VFBX . 100..).( − (mg/100gram sample) ƒ X: ml 2,6 diclorophenol indophenolat natri titrate sample ƒ V: extracting solution volume ( V = 100ml) ƒ v: extracting solution volume to titrate (v = 7ml) ƒ P: amount of sample ( p = 10 gram) ƒ F: mg ascorbic acid equivalent 1ml standard 2,6 diclorophenol indophenolat natri ( F= Y 2 ). • Taste evaluations were carried out by an expert panel of 12 people established at SIAEP laboratory using the hedonic scale (1-9):- 1 = dislike very much 3 = dislike 5 = neither dislike or like 7 = like 9 = like very much RESULTS LOSS IN FRUIT WEIGHT (MOISTURE) Fruit weight loss was greater for the Control and Vacuum Wrapping treatments compared to the Citra Shine Special Wax treatment (Figure 1). Moisture loss for the Vacuum Wrapping and Citra Shine Special Wax treatments was reduced by 13% and 22% respectively compared to the control treatment. The control treatment and Vacuum Wrapping treatment fruit shelf life was 63 days and the fruit treated with Citra Shine Special Wax was 77 days. Control treated fruit at 63 days were extremely shriveled. This was due to sever moisture loss and disease had affected the internal eating quality of the fruit. The Vacuum Wrapped treated fruit were 5 also shriveled, but the fruit had not desiccated to the same degree as the control treated fruit at day 63. The Citra Shine Special Wax treated fruit did not reach the same level of desiccation as the Vacuum Wrapped treated fruit until day 77. The Control treated fruit had the highest rate and the greatest moisture loss of the three treatments (Figure 2). Moisture loss followed a power curve (y=a+bxc) pattern for all treatments. See Figures 2, 3 and 4 below. Day 1 7 14 21 28 35 42 49 56 63 70 77 M oi st ur e lo ss (% ) 0 10 20 30 40 Control Citra Shine Special Vacuum Wrapping Figure 1. Comparison of percentage moisture loss in Nam Roi Pomelo fruit between control, Citra Shine Special Wax and Vacuum Wrap treatments. 6 Days 0 7 14 21 28 35 42 49 56 63 70 77 M oi st ur e lo ss (% ) 0 10 20 30 40 Control (power) y=a+bxc r20.9989934473 a=-3.15094878 b=3.139496644 c=0.602550012 Figure 2. Control treatment, fruit moisture loss over time Days 0 7 14 21 28 35 42 49 56 63 70 77 M oi st ur e lo ss (% ) 0 10 20 30 40 Citra Shine Special Wax (power) y=a+bxc r2=0.99056254 a=-2.33936990 b=2.072603593 c=0.672818004 Figure 3. Citra Shine Special Wax treatment, fruit moisture loss over time 7 Citra Shine Special Wax x column vs y column Days 0 7 14 21 28 35 42 49 56 63 70 77 M oi st ur e lo ss (% ) 0 10 20 30 40 Vacuum Wrapping (power) y=a+bxc r2=0.9910450338 a=-2.33936990 b=2.072603593 c=0.672818004 Figure 4. Vacuum wrapping treatment, fruit moisture loss over time End of shelf life is based on external appearance and the characteristics used are: • fruit have a soft leathery feel • fruit are highly shriveled due to moisture loss • neck of the fruit is sunken and more pronounced • skin colour changes from bright yellow colour to a dull deeper yellow • disease area on infected fruit increase in size rapidly. Internal appearance indicators for end of shelf life is:- • internal browning of the segments and albedo • juice sacks are soft and spongy • juice sacks are not easily separated from the segment • disease areas are visible in the flesh. 8 Figure 5. Control treated fruit day1. Figure 6. Citra Shine Special Wax treated fruit day 1. Figure 7. Vacuum Wrapped treated fruit day 1. 9 Figure 8. Control treated fruit day 63. Figure 9. Citra Shine Special Wax treated fruit day 63. 10 Figure 10. Vacuum wrapped treated fruit day 63. 11 COLOUR READINGS Minolta Chromameter CR 200 was used to determine skin colour changes of the sampled fruit. The colour space measurements are:- L* (positive values indicate lightness and negative values indicate darkness), a* (positive values indicate red as opposed to negative values indicate green), and b* (positive values indicate yellow and negative values indicate blue). Figure 11. L* a* b* colour space difference ∆E* ab Lightness 25% Lightness 50% Lightness 75% Figure 12. Colour diagrammatic representation of L* a* b* colour space values Note: Colour show here may not be a true representation of colour observed by the naked eye as these colours patches are dependent computer, screen and printer settings used to display or print this report. SKIN COLOUR READINGS Traders, collectors, packing agents, wholesalers, retailers and consumers look at the skin colour, and use this as one of the determinates of fruit maturity and ripeness. Therefore, in this experiment we have tried to establish the effects of the anti-transparent and vacuum wrapping on skin colour. 12 Survey work conducted by the CARD Project 05004/ VIE found: • Wholesalers prefer to purchase Nam Roi pomelo fruit that are light green in colour, as this they regard this as a sign of freshness and maturity. If fruit are too yellow they are regarded as being overripe. IF fruit are too green, they are • Wholesalers also prefer to purchase class 1 pomelo fruit with stalks (>10cm) and leaves attached, this is a sign of freshness • Under high temperature conditions in Vietnam pomelo fruit ripen quickly, lose moisture and shrivel, then breakdown due to disease (fruit rots) Table 2 provides a comparison of representative colour space over time taken of the Control, Citra Shine Special Wax and Vacuum Wrapping treatment fruit. Table 2. Skin colour readings from day 1 to day 77 for treatments applied for Nam Roi Pomelo. Day Control Citra Shine Special Wax Vacuum Wrapping 1 Readings L* 51.67; a* -15.85; b* 29.57 L* 53.63; a* -16.17; b* 29.75 L* 58.82; a* -12.41; b* 21.83 7 Readings L* 52.18; a* -15.70; b* 31.43 L* 56.91; a* -15.43; b* 32.36 L* 59.22; a* -12.36; b* 22.95 14 Readings L* 54.09; a* -15.82; b* 32.48 L* 54.58; a* -15.40; b* 31.30 L* 59.86; a* -12.03; b* 24.42 21 Readings L* 56.31; a* -15.09; b* 35.40 L* 57.27; a* -16.12; b* 33.82 L* 61.22; a* -12.42; b* 25.15 28 Readings L* 58.77; a* -15.03; b* 38.20 L* 58.17; a* -15.15; b* 34.41 L* 61.39 a* -12.35; b* 25.75 13 Table 2 (cont). Skin colour readings from day 1 to day 77 for treatments applied for Nam Roi Pomelo. Day Control Citra Shine Special Wax Vacuum Wrapping 35 Readings L* 59.11; a* -13.49; b* 39.99 L* 59.24; a* -15.06; b* 36.49 L* 62.02; a* -11.36; b* 27.56 42 Readings L* 62.35; a* -11.12; b* 43.65 L* 61.56; a* -14.04; b* 37.83 L* 62.63; a* -10.66; b* 28.26 49 Readings L* 63.79; a* -9.09; b* 47.27 L* 61.57; a* -13.06; b* 39.12 L* 58.87; a* -8.89; b* 27.18 56 Readings L*64.58; a* -6.80; b* 47.77 L* 62.55; a* -10.97; b* 40.98 L* 67.44; a*-7.65 ; b* 34.38 63 Readings L* 64.78; a* -4.32; b* 48.85 L* 66.09; a* -8.27; b* 45.40 L* 68.81; a* -5.67; b* 36.79 70 Readings L* 64.16; a* -6.13; b* 45.22 77 Readings L* 68.02; a* -3.18; b* 50.16 The Vacuum Wrapped treated fruit reach a similar skin colour 7 days (1 week) after the Control Treated fruit (Table 2). Fruit treated with Citra Shine Special Wax reach a similar yellow skin colour 14 days (2 weeks) later than the Control treated fruit (Table 2). Therefore, based on skin colour, the Citra Shine Special Wax increased the fruit shelf life by 2 weeks and the Vacuum Wrapping increased shelf life by 1 week. All citrus are non-climacteric fruit, meaning that they ripen gradually over weeks or months. External color changes during ripening, but is a function of climate more than ripeness, and a very poor indicator of maturity. The best indices of maturity for citrus are internal Total Soluble Solids (oBrix or sugar), Titrateable acid content (acid), and the oBrix/acid ratio. 14 SKIN L* COLOUR SPACE We found the L* colour space readings for fruit that were Vacuum Wrapped in a liner of low-density polyethylene plastic film were very slightly altered were due to the reflective nature of the plastic if fruit were measured with the wrapping plastic on. Fruit from all treatments ripened and the skin colour changed from a darker colour (green) to lighter, brighter (Yellow) colour with no adverse affects. Fruit of the Vacuum Wrapping treatment did not change to a lighter colour at the same rate as the Control and Citra Shine Special Wax treated fruit (Figure 13). The Control, Citra Shine Special Wax and Vacuum Wrapped treatments were straight line linear relationships (y=a+bx). See Figures 14, 15 and 16. Initially, the change from a darker colour to a lighter colour was constant for all treatments from day 1 to day 14. The Vacuum Wrapping treatment rate of change slowed until day 49, then increased rapidly to a lighter colour from day 49 to day 63 (Figure 13). Days 0 7 14 21 28 35 42 49 56 63 70 77 L* c ol ou r S pa ce 50 52 54 56 58 60 62 64 66 68 70 Control Citra Shine Special Vacuum Wrapping Figure 13. Comparison of the average L* colour space values for the Control, Citra Shine Special Wax and Vacuum Wrapping Treatments for Nam Roi Pomelo. 15 Days 0 7 14 21 28 35 42 49 56 63 70 77 L* c ol ou r s pa ce 50 55 60 65 70 y=a+bx r2=0.9763023534 a=51.45446086 b=0.233276555 Control Figure 14. Control treatment L* colour space change over time Day vs Traditional method Days 0 7 14 21 28 35 42 49 56 63 70 77 L* c ol ou r s pa ce 50 55 60 65 70 y=a+bx r2=0.9808400384 a=52.613986 b=0.19952952 Citra Shine Special Wax Figure 15. Citra Shine Special Wax treatment L* colour space change over time 16 Days 0 7 14 21 28 35 42 49 56 63 70 77 L* c ol ou r s pa ce 50 55 60 65 70 Vacuum Wrapping y=a+bx r2=0.8837896690 a=57.78614059 b=0.148571500 Figure 15. Vacuum Wrapping treatment L* colour space change over time 17 SKIN A* COLOUR SPACE For the a* colour space (red to green), the Control and Vacuum Wrapped treated fruit remained green until day 28 when the fruit lost the green colour and change to a light yellow colour (Figure 16). All three treatments had similar power curve relationships. The Control treatment changed in colour was slow until day 28, and then increased rapidly until day 63 (Figure 17). The Citra Shine Special Wax treatment increased slowly until day 2, and then increased rapidly until day 77 (Figure 18). The Vacuum Wrapping was the slowest and slowly increased until day 35 and then increased rapidly until day 63 (Figure 19). Days 0 7 14 21 28 35 42 49 56 63 70 77 a* c ol ou r s pa ce -18 -16 -14 -12 -10 -8 -6 -4 -2 Control Citra Shine Special Wax Vacuum Wrapping Figure 16. Comparison of the average a* colour space values for the Control, Citra Shine Special Wax and Vacuum Wrapping Treatments for Nam Roi Pomelo. 18 Days 0 7 14 21 28 35 42 49 56 63 70 77 a* c ol ou r s pa ce -20 -15 -10 -5 0 (power)y=a+bxc r2=0.99255473 a=-16.029398 b=0.0005508 c=2.4113227 Control Figure 17. Control treatment a* colour space change over time Days 0 7 14 21 28 35 42 49 56 63 70 77 a* c ol ou r s pa ce -20 -15 -10 -5 0 (power)y=a+bxc r2=0.96121494 a=-15.867733 b=0.00011966 c=2.66249 Citra Shine Special Wax Figure 18. Citra Shine Special Wax treatment a* colour space change over time 19 Days 0 7 14 21 28 35 42 49 56 63 70 77 a* c ol ou r s pa ce -20 -15 -10 -5 0 (power)y=a+bxc r2=0.98863022 a=-12.452764 b=0. 673678e-06 c=3.1207941 Vacuum Wrapping Figure 19. Vacuum Wrapping treatment a* colour space change over time 20 SKIN B* COLOUR SPACE For the b* colour space readings, all three treatments had a straight line linear relationship and changed colour from blue to yellow colour (Figure 20). The skin b* colour space for the Control treated fruit changed from green to full yellow in 49 days (Figure 21), the Vacuum Wrapping fruit changed from green to full yellow in 56 days (Figure 22) and the Citra Shine Special Wax treated fruit changed from green to full yellow in 63 days (Figure 23). Days 0 7 14 21 28 35 42 49 56 63 70 77 b* c ol ou r s pa ce 25 30 35 40 45 50 55 Control Citra Shine Special Wax Vacuum Wrapping Figure 20. Comparison of the average b* colour space values for the Control, Citra Shine Special Wax and Vacuum Wrapping Treatments for Nam Roi Pomelo. 21 Days 0 7 14 21 28 35 42 49 56 63 70 77 b* c ol ou r s pa ce 25 30 35 40 45 50 55 y=a+bx r2=0.98358781 a=28.74766 b=0.330902975 Control Figure 21. Control treatment b* colour space change over time Days 0 7 14 21 28 35 42 49 56 63 70 77 b* c ol ou r s pa ce 25 30 35 40 45 50 55 y=a+bx r2=0.95109987 a=28.564892 b=0.2463527 Citra Shine Special Wax Figure 22. Citra Shine Special Wax treatment b* colour space change over time 22 Days 0 7 14 21 28 35 42 49 56 63 70 77 b* c ol ou r s pa ce 25 30 35 40 45 50 55 y=a+bx r2=0.91038995 a=20.7378876 b=0.218001025 Vacuum Wrapping Figure 23. Vacuum Wrapping treatment b* colour space change over time 23 TOTAL SOLUBLE SOLIDS (TSS) OR DEGREE BRIX (OBRIX) For this experiment, no relationships could be established between time and change in Total Soluble Solids (oBrix). Figure 24 shows the Control treatment reaching a peak of 13 oBrix on day 49 then dropping sharply to 9 oBrix on days 56 and 63. This drop was due to the fruit being over ripe and breaking down internally. The Citra Shine Special Wax and Vacuum Wrapping treatments oBrix levels continued to rise from day 1 reaching 12 oBrix, even when the fruit had reach the end of their shelf life on day 63 and day 77 respectively (Figure 24). Days 0 7 14 21 28 35 42 49 56 63 70 77 To ta l S ol ul ab le S ol id s (B rix O ) 8 9 10 11 12 13 14 Control Citra Shine Special Wax Vacumm Wrapping Figure 24. Comparison of the average Total Soluble Solids (oBrix) for the Control, Citra Shine Special Wax and Vacuum Wrapping Treatments for Nam Roi Pomelo. TITRATEABLE ACID CONTENT OF FLESH (TA, %) For this experiment no relationships between time and change in titrateable acid content of the flesh was established. For all treatments fruit acid initially increased then dropped sharply. The decrease in acid content is consistent with the literature on post-harvest ripening process of citrus fruit. The acid is used in the respiration process for preserving the citrus fruit. The Control treatment fruit increased in acidity by 16%, peaking on day 21. Fruit then slowly decreased by 3% on day 35. The acidity then dropped sharply by 11% on day 42 before dropping sharply again by 20% on day 63 (Figure 25). Fruit treated with Vacuum Wrapping also increased in acid by 16% on day 14, peaking at 0.86% acid. Fruit then slowly decreased by 6% on day 21, stabilised for 3 weeks before dropping sharply by 25% to reach a low on day 63. The Citra Shine Special Wax treated fruit had a significantly lower acidity. The initial rate of increase was only half that of the Control and Vacuum Wrapping treatments. The acidity level for this treatment 24 peaked at 0.79%, about 9% lower that the Control and Vacuum Wrapping treatments. The acid level decreased at a slower rate compared to the Control and Vacuum Wrapping treatments. Fruit acid then decreased by 25% to be 0.60% on day 77. The amount of decrease is similar to the decrease in acidity for the Control and Vacuum Wrapping treatments, 20% and 25% respectively. Days 0 7 14 21 28 35 42 49 56 63 70 77 Ti tra te ab le A ci d (% ) 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 Day vs Control Day vs Citra Shine Special Wax Day vs Vacuum Wrapping Figure 25. Comparison of the average Titrateable Acid Content of Flesh (TA, %) for the Control, Citra Shine Special Wax and Vacuum Wrapping Treatments for Nam Roi Pomelo. VITAMIN C CONTENT (MG/100G) Vitamin C (ascorbic acid), is one of the most important vitamins found in citrus juices. Temperature and storage time affects Vitamin C content of the pomelo juice. Fructose one of the major sugars found in orange juice, can also cause Vitamin C breakdown. The higher the fructose content the greater the loss of Vitamin C in the fruit. Conversely, higher acid levels of citric and malic acids will stabilize Vitamin C levels. For this experiment, power curve relationships between time and change in Vitamin C content of the flesh was established for the Control and Citra Shine Special Wax Treatments (Figure 23 and 24). For the Vacuum Wrapping treatment, no relationships could be established. 25 Days 0 7 14 21 28 35 42 49 56 63 70 77 Vi ta m in C c on te nt (m g/ 10 0g ) 46 48 50 52 54 56 58 Control Citra Shine Special Wax Vaccum Wrapping Figure 15. Comparison of the average Vitamin C content (mg/100g) between treatments for Nam Roi Pomelo. For the Control treatment the Vitamin C content starting at 50.79mg/100g and by day 63, increased 11% to 56.61mg/100g. The Citra Shine Special Wax treatment dropped slightly, from 50.79 mg/100g on day 1 to 49.43mg/100g on days 35 to 42, before increasing 12% to 57.15mg/100g on day 77. The Vacuum Wrapping treatment remained at about 50.5 mg/100g for the firs 3 weeks (days 7, 14 and 21) before rising to a peak on day 35 of 52.9mg/100g then falling 15% to a low of about 45mg/100g on days 56 and 63. 26 Days 0 7 14 21 28 35 42 49 56 63 70 77 V ita m in C c on te nt (m g/ 10 0g ) 46 48 50 52 54 56 58 60 Control (power) y=a+bxc r2=0.99144725 a=50.515258 b=0.0021529695 c=1.9328596 Figure 23. Control treatment change in Vitamin C content over time Days 0 20 40 60 80 Vi ta ni m C c on te nt (m g/ 10 0g ) 46 48 50 52 54 56 58 60 (power) y=a+bxc r2=0.90240036 a=49.982626 b=0.370021e-07 c=3.8613208 Citra Shine Special Wax Figure 24. Citra Shine Special Wax treatment change in Vitamin C content over time 27 Days 0 7 14 21 28 35 42 49 56 63 70 77 V ita ni m C c on te nt (m g/ 10 0g ) 46 48 50 52 54 56 58 60 Figure 25. Vacuum Wrapping treatment change in Vitamin C content over time TASTE EVALUATIONS For this experiment power curve relationships between time and change in taste of the flesh was established for the Control and Vacuum Wrapping Treatments (Figures 26, 27 and 29). For the Citra Shine Special Wax treatment no relationships could be established (Figure 28). For the Control and Vacuum Wrapping treatments the taste of the fruit decreased with each passing week from rating 5.5 at day 1 to rating 1 at day 63. The Citra Shine Special Wax treatment taste remained constant for the first 3 weeks at rating 5.5 then increased strongly over 4 weeks where it remained until day 77 (Figures 26 and 28). The flesh was still editable for all treatments on day 63 (Figures 30 to 35). 28 Days 0 7 14 21 28 35 42 49 56 63 70 77 Ta st e ev al ua tio n (h ed on ic s ca le 1 -9 ) 0 1 2 3 4 5 6 7 8 Control Citra Shine Special Wax Vacuum Wrapping Figure 26. Comparison of the average taste evaluations for the Control, Citra Shine Special Wax and Vacuum Wrapping Treatments for Nam Roi Pomelo. Days 0 7 14 21 28 35 42 49 56 63 70 77 Ta st e ra tin gs (h ed on ic s ca le 1 -9 ) 0 2 4 6 8 y=a+bx3 r2=0.95187934 a=5.2677875 b=-1.917299e-05 Control Figure 27. Control treatment change in taste ratings over time 29 Days 0 7 14 21 28 35 42 49 56 63 70 77 Ta st e ra tin gs (h ed on ic s ca le 1 -9 ) 0 2 4 6 8 Figure 28. Citra Shine Special Wax treatment change in taste ratings over time Days 0 7 14 21 28 35 42 49 56 63 70 77 Ta st e ra tin gs (h ed on ic s ca le 1 -9 ) 0 2 4 6 8 y=a+bx3 r2=0.8752014484 a=4.9926205 b=1.2851301e-05 Vacuum Wrapping Figure 29. Vacuum Wrapping treatment change in taste ratings over time 30 Figure 30. Control treatment fruit day 63 Figure 31. Citra Shine Special Wax treatment fruit day 63 31 Figure 32. Vacuum Wrapping treatment fruit day 63 Figure 33. Control treatment fruit segment day 63 Figure 34. Citra Shine Special Wax treatment fruit segment day 63 32 Figure 35. Vacuum Wrapping treatment fruit segment day 63 DISEASES Several post-harvest diseases are initiated during fruit growth or the pre-harvest phase and affect the postharvest shelf life of the pomelo fruit. Some of these diseases are; • Diplodia (Stem End Rot) • Phomopsis • Alternaria • Botrytis • Colletotrichum • Phytophtyora So called stem end rots of citrus are usually caused by Diplodia and Phomopsis and occur in regions with a high rainfall. Lesions of the fruit become dark, leathery and sunken and the fungus grows through the centre of the fruit causing considerable internal breakdown and a reddish brown discolouration. Several other diseases originate during the post-harvest handling phase. These diseases enter through wounds acquired during the harvesting, handling, packing and transport. These so called “wound pathogens” are: • Penicillium digitatum (Green Mould) • Penicillium italicum (Blue Mould) • Geotrichum (Sour Rot) • Trichoderma (Trichoderma Rot) These pathogens infect wounds, invaliding at least 2-3mm deep into the peel of the fruit. These pathogens may also invade through insect damage sites. The most common diseases are, Green Mould and Blue Mould. Some of the diseases found on fruit during this experiment are shown in Figures 36 through to 42. 33 Figure 2.6 Vacuum Wrapped treated fruit severely affected by Diplodia or Stem End Rot Figure 37. Control (Left) and Citra Shine Special Wax (Right) treated fruit affected with Phomopsis 34 Figure 38. Citra Shine Special Wax (Right) treated fruit affected with Phomopsis Figure 39. Citra Shine Special Wax (Right) treated fruit affected with Phomopsis Figure 40. Citra Shine Special Wax Treated fruit being attached by Phytophtyora (Brown Rot). (Note the white fungal growth coming from he stem and top of fruit) 35 Figure 41. Control treated fruit Penicillium italicum (Blue Mould) 36 Figure 42. Citra Shine Special Wax treated fruit affected with damaged oil glands and early stages of attack by Diplodia 37 DISORDERS After about 35 days, pomelo fruit that are left in one position became flat on that surface on which it was sitting. All fruit from the three treatments showed this symptom in this experiment. Figure 43. Note the flat surface on the base of the Citra Shine Special Wax pomelo fruit. CONCLUSIONS All citrus are non-climacteric fruit, meaning that they ripen gradually over weeks or months. The best indices of maturity for citrus are internal Total Soluble Solids (oBrix or sugar), Titrateable acid content (acid), and the oBrix/acid ratio which has been well established in the literature and used by many countries including Australia and the United States of America as a test of maturity and harvest index. All of the farmers, collectors, traders, packing agents, wholesalers, retailers and consumers use colour as one of the indicators of maturity in the Mekong River Delta of southern Vietnam. This experiment establishes that skin colour is not a good indicator of Nam Roi pomelo fruit maturity. The oBrix or sugar and acid content continued to increase even after the fruit were harvested. This may be due to the significant moisture loss which occurs within the pomelo fruit after harvest and the concentration of sugars and acid in the fruit. Compared to the Control treatment, the Vacuum Wrapping and Citra Shine Special Wax treatments significantly reduced fruit moisture lost. Pomelo fruit treated with Citra Shine Special Wax increased the shelf life of pomelo fruit based on fruit colour. The increase was about 2 weeks compared to the control and Vacuum Wrapping treated fruit. For the L* colour space (dark to light) the Vacuum Wrapping treatment did slow the rate at which the fruit lightened in colour (green to yellow) compared to the Control and Citra Shine Special Wax treated fruit. Changes in a* colour space (green to red) and b* (blue to yellow) colour space was significantly slower for the Citra Shine Special Wax and Vacuum Wrapped treated fruit. The change from green to yellow was about one week later for the Citra Shine Special Wax and Vacuum Wrapped treated fruit compared to the Control treated fruit. This delay in colour change may have some affect on the supply chains operating in the Mekong River Delta in southern Vietnam by allowing traders, collectors, packing agents and wholesalers to hold fruit 38 back from marketing for about a week. This is a significant advantage considering there are no cool chains or other post harvest treatments applied to pomelo fruit before marketing. Peak oBrix levels for the Vacuum Wrapping were not reached until 2 weeks after the Control treated fruit, day 63 and day 49 respectively. Peak oBrix levels for the Citra Shine Special Wax treated fruit were not reached until 4 weeks after the Control treated fruit, day 77 and day 49 respectively. These two treatments delayed the ripening of the pomelo fruit and increasing the pomelo fruit shelf life. Taste evaluations showed that the fruit treated with Citra Shine Special Wax were significantly better than the Control and Vacuum Wrapping treated fruit. At day 63 the Citra Shine Special Wax treated fruit rated at 5.5, (neither liked nor disliked), whilst the Control and Vacuum Wrapping treated fruit rated 1, (disliked very much). The highly variability in the maturity of the fruit and the small sample size used in this experiment meant that we were unable to establish a relationship between oBrix and acid content of the fruit. Further studies are warranted to see if there is a relationship the oBrix and acid content to develop a reliable maturity index for pomelo in the Mekong River Delta of southern Vietnam. Vacuum Wrapping and moisture condensation inside the wrapping also played a significantly role in increasing the incidence of disease. Fruit that are vacuumed wrapped, or have a special anti- transparent applied must have no physical damage to the surface of the skin. Fruit must also be sanitised thoroughly to eliminate any possible disease infection before applying postharvest treatments. This is especially critical for fruit destined for export due to quarantine requirements of importing countries and developing a reliable trade mark and reputation for Vietnamese pomelo fruit. Further studies are also needed to test the effectiveness of these treatments on cool chain exported pomelo fruit as there may be additional benefits in delaying the ripening by cooling the fruit and increased shelf life.