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Fruit Juices and Puree Technology
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Fruitjuicesandpureetechnology:examplesofappliedresearch
CONFERENCEPAPER·JUNE2015
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RobertoMassini
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Fruit juices and puree technology:examples of applied research
Roberto Massiniformerly professor of Food Science & Technologyat the University of Parma, Italy
Africa's Big Seven: 21-23 June 2015, Johannesburg, South Africa"Made in Italy" Technology Pavilion Workshops
21 June 2015THE INCREASING CONSUMPTION OF JUICES WORLDWIDE AND THE ROLE OF TECHNOLOGIES
New developments and techniques for juices and puree processing and packagingand new products creating opportunities for growth
Pomegranate (Punica granatum) juice
Increasing request of pomegranate juice as a healthy food on the northern hemisphere market.
Increasing production of pomegranate in southern hemisphere and, especially, in South Africa.
Health benefits of pomegranate are due to high polyphenols content (principally anthocyanins and phenolic acids).Anthocyanins from pomegranate fruit possess higher antioxidant activitythan vitamin-E (α-tocopherol), β-carotene, and ascorbic acid.
Compared to the pulp, peels contain more and different bioactive compounds (principally hydrolyzable tannins), which can increase the functional properties of the juice.
Husk
Peels
Arils (seeds surrounded by juicy aril)
highest phenol content, butbitter and astringent taste
To maximizing functional propertieswhile preserving sensory acceptability:
Arils separation: by a conventional grape destemmer.• Changing parameters as shaft velocity, drum velocity and blades position it
is possible to optimize the skin and connectival tissue separation.Juice cold extraction: by a screw press.• The presence of a suitable amount of peels allows obtaining juice with
high antioxidant activity, but keeping the bitterness under the threshold perceived as negative by the consumers.
Juice enzymation: by pectolytic enzymes. • By adopting appropriate operating conditions, the turbidity of the juice is
reduced without reducing, but increasing, the total polyphenols content.• A slight turbidity of the juice must be accepted, because a further stage of
flocculation or microfiltration would severely reduce antioxidant capacity.Thermal treatment: by aseptic processing and packaging.• Full deaeration and HTST conditions allow limiting thermal damage.
Passive heat transfer enhancement for HTST
For three fruit products: cloudy orange juice, apricot and apple puree, the heat transfer enhancement by helically corrugated shell and tube wasevaluated with respect to smooth wall tube.
Pilot plant layout
Corrugated tube
OVERHEATED WATER PUMP
HEATER WATER/STEAM
EXSPANSION VESSEL
STEA
M
WATER
BACKPRESSURE VALVE
COOLING SECTION
HEATING SECTION
WA
TER
PRO
DU
CT
FEEDING TANK
PUMP
OVERHEATED WATER PUMP
HEATER WATER/STEAM
EXSPANSION VESSEL
STEA
M
WATER
BACKPRESSURE VALVE
COOLING SECTION
HEATING SECTION
WA
TER
PRO
DU
CT
FEEDING TANK
PUMP
0.00.51.01.52.02.53.03.54.0
0 5000 10000 15000 20000
Average Reynolds number
Pres
sure
loss
es (b
ar)
Not corrugated wall heating Corrugated wall heatingNot corrugated wall cooling Corrugated wall cooling
0500
100015002000250030003500
0 5000 10000 15000 20000
Average Reynolds number
Ove
rall
heat
tran
sfer
co
effic
ient
(W/m
2 ·K)
Not corrugated wall pipes Corrugated wall pipesNot corrugated wall pipes Corrugated wall pipes
Cloudy Orange juice (11.2 °Bx):Flow index n = 1.0 (25-65°C) Newtonian flow behaviourConsistency coefficient K = 0.0019 (25°C) – 0.0008 (65°C) LOW
Variations of the overall heat transfer (a) and pressure drop (b) as a function of the generalized Reynolds number
The increase of the overall heat transfer coefficient obtained with corrugation is modest, because Newtonian fluids at low viscosity have turbulent flow even with lower flow rates. However, it is relevant the increase of pressure drops.
a b
Apple puree (11.8°Bx):Flow index n = 0.322 (25°C) – 0.341 (65°C) Pseudoplastic flow behaviourConsistency coefficient K = 9.9957 (25°C) – 7.1437 (65°C) HIGH
Variations of the overall heat transfer (a) and pressure drop (b) as a function of the generalized Reynolds number
The corrugation effect for heat transfer resulted almost of no value, because for high consistency fluid the flow can be considered always laminar. The increase in pressure drops is not considerable.
0
500
1000
1500
2000
0 20 40 60 80 100
Average Reynolds number
Ove
rall
heat
tran
sfer
co
effic
ient
(W/m
2 ·K)
Not corrugated wall pipes Corrugated wall pipesNot corrugated wall pipes Corrugated wall pipes
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100
Average Reynolds number
Pres
sure
loss
es (b
ar)
Not corrugated wall heating Corrugated wall heatingNot corrugated wall cooling Corrugated wall cooling
a b
Apricot puree (10.8°Bx) :Flow index n = 0.273 (25°C) – 0.347 (65°C) Pseudoplastic flow behaviourConsistency coefficient K = 1.7641 (25°C) – 0.8090 (65°C) MEDIUM
Variations of the overall heat transfer (a) and pressure drop (b) as a function of the generalized Reynolds number
For this intermediate consistency fluid the increase in performance of the corrugated wall pipe is noticeable, because the transition from laminar to turbulent flow. Even more remarkable is the effect for the pressure drops.
0500
1000150020002500300035004000
0 500 1000 1500 2000 2500 3000
Average Reynolds number
Ove
rall
heat
tran
sfer
co
effic
ient
(W/m
2 ·K)
Not corrugated wall pipes Corrugated wall pipesNot corrugated wall pipes Corrugated wall pipes
0.0
1.0
2.0
3.0
4.0
5.0
0 500 1000 1500 2000 2500 3000
Average Reynolds number
Pres
sure
loss
es (b
ar)
Not corrugated wall heating Corrugated wall heatingNot corrugated wall cooling Corrugated wall cooling
a b
The corrugated tubes may or may not increase the heat transfer according to the rheology of the treated product. More precisely, there is a real advantage only if, other conditions being equal, the corrugation induces the transition from laminar to turbulent flow.On the other hand the corrugated tubes cause an unfavorable, more or less pronounced, increase in pressure drop.
Product’s rheological behavior More suitable heat exchanger• Newtonian, low viscosity • Smooth wall tube• Pseudoplastic, high consistency • Scraped surface• Pseudoplastic, medium consistency • Corrugated wall tube
Foreward control to reduce thermal damageSimplified diagram of a process system commonly used for fruit juice
HEAT EXCHANGER+ -Tsp
Tout
productchanges:∆Tin , ∆Mp , ∆cp
heating fluidchanges:∆Thf / ∆Mhf
e mPID VALVE
change: ∆OHTC
PLC
RTD
Current control of the heating unit: reactive "feedback"
Undershoot
Range of normal variability
When incoming variables undergo rapid transients, feedback control is not able to maintain outlet temperature within a narrow band.To avoid frequent recycle of the product, the temperature set point must be very oversized, with a systematic large overprocessing.
HEAT EXCHANGERVALVE+ -
Tsp
Tout
++
FEEDFORWARDin PC/PLC
PID in PLC RTD
∆Thf/∆Mhf
RTDT / Mmeter
Flow-meter
∆Mp
∆Tin
change: ∆OHTC
change: ∆cp
Integration with predictive control to manage properly the fast transients
10
Feedback Control
Feedback + FeedforwardControl
The predictive control allows to remarkably reduce the average heating temperature of the product and this, in addition to reducing the thermal damage to the nutritional and sensory properties, reduces the frequency of stop of production necessary to clean the plant.However, despite the low cost of the processing system adaptation, the feedforward control is not used.Often, on the other hand, in the PID feedback control the derivative function is disabled.This can only be justified by knowledge reasons:
- While it is only requested a generic technical expertise to set up and tune the feedback control system, the feedforward operation algorithms are based on the physical laws of heat exchange.
- The application of a heat treatment largely oversized creates a strong but false security, because it diverts attention from the overall needs of process control.
All cold to preserve the natural properties
The inactivation of microorganisms in juices by Supercritical carbon dioxide(ScCO2) nonthermal processing was developed to combine it with the cold extraction of the fruit and the refrigerated storage of final product.
Pilot plant for ScCO2 processing and aseptic packaging
31.1°C
73.8
bar
Phase diagram for carbon dioxide
The cold pasteurization with ScCO2 has been studied by many authors, but with discordant results and, however, by using small laboratory apparatus.Our continuous flow pilot plant has capacity up to 40 l/h and has been designed to make it scalable up to productive sizes.
A supercritical fluid has high diffusivity such as a gas, but is a solvent such as a liquid.Theoretically ScCO2 can destroy microbial cells with the following effects:- Solubilization of cell wall components;- Acid denaturation of cytoplasm components;- Laceration of the cell in the decompression phase.
After many experiments were identified plant and operating conditions adequately effective.In both clear and turbid apple juice (pH = 3,25 - 9,8 °Bx), the ScCO2treatment for 90 seconds at 40°C and 100 bar reduced by at least 99.999% or 5 logs the inoculum of three standard micro-organisms:- Listeria innocua, - Lactobacillus plantarum, and - Saccharomices cerevisiae. Treatment with ScCO2 has a positive effect on the texture of apple juice, by increasing the consistency and the degree of pseudoplasticity.Because pectolytic and oxidative enzymes are not inactivated, it is necessary to remove air from the headspace of package and store the product at refrigeration temperatures.These conditions, however, are necessary to ensure the retention of excellent quality properties.
