Modelling and optimization of active modified atmosphere packaging for pomegranate arils

Belay, Zinash Assefa (2017-12)

Thesis (PhD (Food Sc))--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Active modified atmosphere packaging (active-MAP) is a well-proven postharvest technology used to preserve the quality and extend the storage and shelf life of fresh fruit under optimally designed conditions. Successful active-MAP design can be achieved by the mathematical integration of produce physiological characteristics, packaging material properties, and equilibrium gas mixture suitable for the product. The mechanisms by which active-MAP influences fruit quality involve physiological and enzymatic reactions that can be accelerated or reduced depending on the environmental conditions during storage. Therefore, understanding the experimental design and fundamental physiological processes occurring during storage condition are important in the development of an optimal produce-specific active-MAP. Low O2 limit for pomegranate arils was identified at 5 and 10 °C and the responses were monitored using real time respiration rate (RR), respiratory quotient (RQ), emission of volatile organic compounds (VOCs) and microbial growth. The results showed that pomegranate arils could tolerate down to 2.18% O2 during storage at 5 °C and 2.28% O2 at 10 °C. These findings highlighted the importance of selecting appropriate MAP materials with desired permeability to alleviate rapid depletion of O2 and excessive accumulation of CO2 at 10 °C inside the package. The impact of active-MA on quality attributes of ‘Wonderful’ pomegranate arils were investigated at cold (5 °C, 95 ± 2% RH) and ambient storage (20 °C, 65 ± 2% RH) conditions. Low O2 (5-10%) atmospheres significantly maintained antioxidant properties of arils, whereas significantly lower aerobic mesophilic bacteria, yeast and mould counts were found at super-atmospheric O2 (70%). Storing pomegranate arils under ambient condition resulted in quality deterioration and short shelf life. The effects of low O2 and super-atmospheric O2 on RR of ‘Wonderful’ pomegranate arils were analysed at 5 °C. Michaelis-Menten (MM) enzyme kinetic models were applied to determine the inhibition effects of CO2 concentration on O2 consumption rate. The results showed that both storage atmosphere and temperature had significant effects on aril RR. The MM competitive inhibition model best described the effect of CO2 on O2 consumption rate at low O2 and super-atmospheric O2 (R2 > 99%). The findings showed that super-atmospheric O2 had no effect to retard the metabolic process. A simplex lattice mixture design (SLMD) approach was applied to optimize gas composition for storing arils, and effects of temperature on the optimum gas was studied. A special cubical model were developed for the responses (RR, RQ, ethylene production rate and microbial quality) and the coefficients of model parameter estimates (β1, β2, β3, β12, β13, β23 and β123) and ternary contour plots were characterised. The predicted optimium gas mixture (O2:CO2) was 2% O2:18% CO2); and at this atmosphere, the minimum values of RR were 0.26 mL O2 kg-1 h-1 and 0.78 mL CO2 kg-1 h-1, while ethylene production rate was below the detection limit. Under these conditions, the growth of aerobic mesophilic bacteria (3.9 log CFU mL-1), yeast (3.8 log CFU mL-1) and mould (2.3 log CFU mL-1) were quantified. Increasing the storage temperature by 10 °C resulted in a threefold increase in aril RR. Using the same SLMD approach, the optimum gas composition required to maintain individual quality attributes was predicted. Variation in optimal gas mixture for individual quality attributes of arils were observed. According to the model parameter estimates, the optimum gas composition (O2:CO2) was established (6-7% O2:7-8% CO2) for individual sugars, organic acids, antioxidants and colour attributes. The optimum gas composition to maintain aril hardness and volatile compounds (monoterpene and ketones) was 2% O2 and 18% CO2. On the other hand, the optimum atmosphere for aldehydes was 2% O2 and 2% CO2. An integrated designing approach was applied to configure a packaging system for arils capable of modifying atmosphere and in-package relative humidity by designing modified atmosphere humidity package (MAHP) system. Cellulose based NatureFlex® (NF) film, bi-axial oriented polypropylene (BOPP) (PF) film and combinations of the two films were used. The 100% NF package created the lowest in-package RH (60-66%) and the highest reduction of O2, which resulted in arils dryness during storage. The 100% BOPP film resulted in saturated RH and in-package water vapour condensation. The optimized package design using 66% PF and 33% NF films best maintained the overall quality of pomegranate arils. This study demonstrated the potential of SLMD as an innovative tool to optimize the gas composition and improve packaging design for effective cold storage of minimally-processed fresh produce such as pomegranate arils. The results obtained also provide new information on the optimum condition required to maintain specific quality parameters for the commercialization of active-MA for packaging and marketing of pomegranate arils.

AFRIKAANSE OPSOMMING: Aktiewe gemodifiseerde atmosfeerverpakking (aktiewe-MAP) is 'n beproefde na-oes tegnologie wat gebruik word om die kwaliteit van vars vrugte in stand te hou, en die berging en rakleeftyd onder optimaal ontwerpte toestande te verleng. Suksesvolle aktiewe-MAP ontwerp kan bereik word deur wiskundige integrasie van fisiologiese eienskappe, verpakkingsmateriaal eienskappe en ewewig gasmengsel wat geskik is vir die produk. Die meganismes waardeur aktiewe-MAP die vrugkwaliteit beïnvloed behels fisiologiese en ensimatiese reaksies wat versnel of verminder kan word, afhangende van die omgewingstoestande tydens berging. Daarom is die begrip van eksperimentele ontwerp en fundamentele fisiologiese prosesse wat tydens bergingstoestande plaasvind, belangrik in die ontwikkeling van 'n optimale produkspesifieke aktiewe-MAP. ‘n Lae O2-limiet van 5 en 10 °C is vir granaat-arils geïdentifiseer en die respons is gemonitor deur gebruik te maak van waretyd respirasie tempo (RR), respirasie kwosiënt (RQ), emissie van vlugtige organiese samestellings (VOCs) en mikrobiese groei. Die resultate het getoon dat granaat arils tot 2.18% O2 kan verdra tydens berging by 5 °C en 2.28% O2 by 10 °C. Hierdie bevindinge beklemtoon die belangrikheid om die gepaste MAP materiaal met die gewenste deurlaatbaarheid te kies, om by 10 °C vinnige uitputting van O2 en oormatige ophoping van CO2 binne die verpakking te verlig. Die impak van aktiewe-MA op kwaliteitseienskappe van ‘Wonderful’ granate is ondersoek teen koue (5 °C, 95 ± 2% RH) en omringende (20 °C, 65 ± 2% RH) bergingstoestande. Lae atmosferiese O2 (5-10%) het die antioksidante eienskappe van arils aansienlik gehandhaaf, terwyl aansienlike laer vlakke van aërobiese mesofiele bakterieë, gis en swam tellings by super-atmosferiese O2 (70%) gevind is. Granate wat onder omgewingstoestande geberg is, het gelei tot 'n afname in die kwaliteitsgehalte en 'n kort rakleeftyd. Die effekte van lae O2 en super atmosferiese O2 op RR van 'Wonderful' granate is by 5 °C geanaliseer. Michaelis-Menten (MM) ensiem-kinetiese modelle is toegepas om die inhibisie-effekte van CO2-konsentrasie op O2-verbruikerstempo te bepaal. Die resultate het getoon dat beide bergingsatmosfeer en -temperatuur beduidende effekte op aril RR gehad het. Die MM-mededingende inhibisie model het die effek van CO2 op O2-verbruikerstempo by lae O2 en super-atmosferiese O2 (R2 > 99%) die beste beskryf. Die bevindinge het getoon dat super-atmosferiese O2 geen effek gehad het om die metaboliese proses te vertraag nie. 'n Simpleks rooster mengsel ontwerp (SLMD) benadering is aangewend om die gas samestelling vir die berging van arils te optimaliseer, en die effekte van temperatuur op die optimale gas samestelling te ondersoek. 'n Spesiale kubiese model is ontwikkel vir die veranderlikes (RR, RQ, etileenproduksietempo en mikrobiese gehalte) en die koëffisiënte van modelparameterskattings (β1, β2, β3, β12, β13, β23 en β123) en ternêre kontoerplotte is gekenmerk. Die voorspelde optimale gasmengsel (O2:CO2) was 2% O2: 18% CO2; En by hierdie atmosfeer was die minimum RR waardes 0.26 ml O2 kg-1 h-1 en 0.78 ml CO2 kg-1 h-1, terwyl die etileenproduksietempo 0,0 μL kg-1 h-1 was. Onder hierdie toestande is die groei van aërobiese mesofiele bakterieë (3.9 log CFU mL-1), gis (3.8 log CFU mL-1) en swamme (2.3 log CFU mL-1) gekwantifiseer. Die 10 °C verhoging in bergingstemperatuur het gevolglik die RR van arils drievoudig laat toeneem. Die vereiste optimale gassamestelling om individuele kwaliteitseienskappe te handhaaf, is met dieselfde SLMD-benadering voorspel. Die optimale gasmengsel vir individuele kwaliteitskenmerke van arils het gevarieer. Volgens die skattings van die modelparameters is die optimale gassamestelling (O2: CO2) vasgestel (6-7% O2: 7-8% CO2) vir individuele suikers, organiese sure, antioksidante en kleur-eienskappe. Terwyl die optimale gassamestelling om aril hardheid en vlugtige verbindings (VOCs) soos monoterpeen en ketone te onderhou, 2% O2 en 18% CO2 was. Aan die ander kant was die optimale atmosfeer vir aldehiede 2% O2 en 2% CO2. 'n Geïntegreerde ontwerpbenadering is toegepas om 'n verpakkingstelsel op te stel vir arils waarvan die binne-verpakking relatiewe humiditeit (MAHP) en gas samestelling verander kan word. Sellulose-gebaseerde NatureFlex® (NF) film, bi-aksiale georiënteerde polipropileen (BOPP) (PF) film en kombinasies van die twee films is gebruik. Die 100% NF-verpakking het die laagste binne-verpakking RH (60-66%) en die hoogste verlaging van O2 geskep, wat die arils uitgedroog het tydens die bergingsperiode. Die 100% BOPP film het gelei na versadigde RH en binne-verpakking waterdamp kondensasie. Die geoptimaliseerde verpakkingsontwerp wat 66% PF en 33% NF-films gebruik, het die algehele gehalte van granaat arils die beste behou. Hierdie studie het die potensiaal van SLMD as 'n innoverende instrument getoon om die gassamestelling te optimaliseer en die verpakkingsontwerp te verbeter, vir effektiewe verkoeling van minimaal verwerkte vars produkte soos granate. Hierdie resultate verskaf ook nuwe inligting oor die vereiste optimale toestand om spesifieke gehalte-parameters te handhaaf vir die kommersialisering van aktiewe MA vir verpakking en bemarking van granate.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102629
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