Báo cáo nghiên cứu khoa học " MAINTAINING FRUIT QUALITY AND INCREASING SHELF LIFE OF POMELO IN THE MEKONG DELTA OF SOUTHERN VIETNAM " pot

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, Queensland Department of Primary Industries and Fisheries (DPI&F) , Maroochy Research Station, PO Box 5083 SCMC, Queensland, Australia, 4560 Southern Sub-Institute of Agricultural Engineering and Post-Harvest Technology (SIAEP), 54 Tran Khanh Du Street, District 1, Ho Chi Minh City, Vietnam 1 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, Queensland Department of Primary Industries and Fisheries (DPI&F) , Maroochy Research Station, PO Box 5083 SCMC, Queensland, Australia, 4560 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 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 to 2%, but surveys found that it is often above 10% due to moisture loss, handling damage and disease attack Therefore, this CARD Project set up experiments to evaluate the benefits of developing new postharvest 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 days for 12 weeks Treatments applied were: Control 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 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 drops of phenolphalayene indicator was added and titrated with Sodium Hydroxide (NaOH) 0.1 normal solution, until colour change occurred • • 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 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 minutes to occur o Count amount of 2,6 DCPIP need to titrate 1mg acid ascorbic + Take ml standard acid ascorbic solution add ml Metaphosphoric-acetic +Titrate with 2,6 diclorophenol indophenolat natri until fast pink colour appears in about minutes (note number ml : y) o Titrate blank sample with 2,6 diclorophenol indophenolat natri until fast pink colour appears This takes about minutes to occur (note number ml = B) Calculation Content of Vitamin C = • ( X − B).F V 100 (mg/100gram sample) v.P X: ml 2,6 diclorophenol indophenolat natri titrate sample V: extracting solution volume ( V = 100ml) v: extracting solution volume to titrate (v = 7ml) P: amount of sample ( p = 10 gram) F: mg ascorbic acid equivalent 1ml standard 2,6 diclorophenol indophenolat natri ( F= ) Y 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 = dislike = neither dislike or like = like = 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 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, and below 40 Control Citra Shine Special Vacuum Wrapping Moisture loss (%) 30 20 10 14 21 28 35 42 49 56 63 70 77 Day Figure Comparison of percentage moisture loss in Nam Roi Pomelo fruit between control, Citra Shine Special Wax and Vacuum Wrap treatments 40 Control Moisture loss (%) 30 (power) y=a+bxc r20.9989934473 a=-3.15094878 b=3.139496644 c=0.602550012 20 10 0 14 21 28 35 42 49 56 63 70 77 Days Figure Control treatment, fruit moisture loss over time 40 Citra Shine Special Wax Moisture loss (%) 30 (power) y=a+bxc r2=0.99056254 a=-2.33936990 b=2.072603593 c=0.672818004 20 10 0 14 21 28 35 42 49 56 63 70 77 Days Figure Citra Shine Special Wax treatment, fruit moisture loss over time 40 Vacuum Wrapping (power) y=a+bxc r2=0.9910450338 a=-2.33936990 Citra Shine Special Wax b=2.072603593 x column vs y column c=0.672818004 Moisture loss (%) 30 20 10 0 14 21 28 35 42 49 56 63 70 77 Days Figure 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 Figure Control treated fruit day1 Figure Citra Shine Special Wax treated fruit day Figure Vacuum Wrapped treated fruit day Figure Control treated fruit day 63 Figure Citra Shine Special Wax treated fruit day 63 Figure 10 Vacuum wrapped treated fruit day 63 10 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 0.90 Titrateable Acid (%) 0.85 0.80 0.75 0.70 0.65 Day vs Control Day vs Citra Shine Special Wax Day vs Vacuum Wrapping 0.60 0.55 14 21 28 35 42 49 56 63 70 77 Days 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 24 58 Control Citra Shine Special Wax Vaccum Wrapping Vitamin C content (mg/100g) 56 54 52 50 48 46 14 21 28 35 42 49 56 63 70 77 Days 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 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 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 25 60 Vitamin C content (mg/100g) 58 Control c (power) y=a+bx r2=0.99144725 a=50.515258 b=0.0021529695 c=1.9328596 56 54 52 50 48 46 14 21 28 35 42 49 56 63 70 77 Days Figure 23 Control treatment change in Vitamin C content over time 60 Vitanim C content (mg/100g) 58 Citra Shine Special Wax c (power) y=a+bx r =0.90240036 a=49.982626 b=0.370021e-07 c=3.8613208 56 54 52 50 48 46 20 40 60 80 Days Figure 24 Citra Shine Special Wax treatment change in Vitamin C content over time 26 60 Vitanim C content (mg/100g) 58 56 54 52 50 48 46 14 21 28 35 42 49 56 63 70 77 Days 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 to rating at day 63 The Citra Shine Special Wax treatment taste remained constant for the first weeks at rating 5.5 then increased strongly over 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) 27 Taste evaluation (hedonic scale 1-9) Control Citra Shine Special Wax Vacuum Wrapping 0 14 21 28 35 42 49 56 63 70 77 Days Taste ratings (hedonic scale 1-9) Figure 26 Comparison of the average taste evaluations for the Control, Citra Shine Special Wax and Vacuum Wrapping Treatments for Nam Roi Pomelo Control y=a+bx3 r2=0.95187934 a=5.2677875 b=-1.917299e-05 0 14 21 28 35 42 49 56 63 70 77 Days Figure 27 Control treatment change in taste ratings over time 28 Taste ratings (hedonic scale 1-9) 0 14 21 28 35 42 49 56 63 70 77 Days Taste ratings (hedonic scale 1-9) Figure 28 Citra Shine Special Wax treatment change in taste ratings over time Vacuum Wrapping y=a+bx3 r2=0.8752014484 a=4.9926205 b=1.2851301e-05 0 14 21 28 35 42 49 56 63 70 77 Days Figure 29 Vacuum Wrapping treatment change in taste ratings over time 29 Figure 30 Control treatment fruit day 63 Figure 31 Citra Shine Special Wax treatment fruit day 63 30 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 31 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 32 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 33 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) 34 Figure 41 Control treated fruit Penicillium italicum (Blue Mould) 35 Figure 42 Citra Shine Special Wax treated fruit affected with damaged oil glands and early stages of attack by Diplodia 36 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 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 37 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 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 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 antitransparent 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 38 .. .MAINTAINING FRUIT QUALITY AND INCREASING SHELF LIFE OF POMELO IN THE MEKONG DELTA OF SOUTHERN VIETNAM Robert Nissen1, Nguyen Duy Duc2, Ms San Tram... on skin colour, the Citra Shine Special Wax increased the fruit shelf life by weeks and the Vacuum Wrapping increased shelf life by week All citrus are non-climacteric fruit, meaning that they... 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