Processing Natural Orange Juice
From an industrial point of view we can consider an orange to be a composite of 43% juice and 57% peel and pulp. These figures can vary considerably and no two oranges are the same, with differences due to varieties, season and weather and source. The separation processes used, any thermal treatments received and the storage conditions of the juice will also have an effect.
A key issue in the industrial juice sector is the formation of aromatic derivative compounds. Consequently, a number of different processes are used to combat this problem. To evaluate the effectiveness of the treatments applied we must measure the quality of the resultant product. The parameters used to evaluate quality include:
- Dry extract
- Degrees Brix
- Acidity (Citric Acid)
- Essential Oils
- Index of maturity
- Limonin content
- Pectinesterase (PME)
- Formal Index
- Hydroxymethylfurfural (HMF)
- Ascorbic Acid (Vitamin C)
The influence of the thermal treatments in the quality of orange juice
The principal objectives of the thermal treatments are:
- Inactivation of the enzyme Pectinesterase (PME). This is achieved by subjecting the juice to a temperature of 98°C for 30 seconds.
- Prevent of Hydroxymethylfurfural (HMF). This requires short periods of thermal treatment to be used.
Long treatment times increase the amount of HMF and reduce the quality of the resulting product.
Objectives of the process used by HRS Heat Exchangers
The objectives, when designing an orange juice processing plant, are:
Objective 1- To maximise the quality and the taste of the juice
HRS Heat Exchangers uses technology which allows the application of reduced thermal treatment times which give good results when the quality parameters are evaluated for the final product.
Objective 2 – To minimise energy consumption
HRS Pasteurisers recover up to 85% of the energy during the process, which contributes enormously to a reduction in overall processing costs. The energy necessary for the evaporation processes normally comes from the drying plant, giving additional savings.
Objective 3 – Exploitation of orange by-products
The dried peel of the orange produced in the final part of the process is a valuable product which can be used in the chemical industry.
Objective 4 – Digital control of the factory
The use of electronic control technologies and the Internet allows the user to monitor the processes and product flow rates in real time and on remote terminals. From the control cabinet the plant operators can monitor, from any computer terminal with an internet connection, the current state of the factory and any incidents or deviations in the production process.
Three basic disciplines are used in the process:
- Mass transfer
- Heat transfer
- Squeezing the orange
Principal components of the HRS Heat Exchangers’ solution
The essential aspects and technologies involved in the HRS Heat Exchangers processing plant are as follows:
Firstly the oil is removed. This process is carried out without causing damage to the fruit. It is done to avoid undesirable flavours and obtain the highest possible level of aldehydes.
Secondly the juice is extracted. The technology used involves cutting and squeezing the orange and is different to many of the In-line systems used. The HRS process does not damage the peel and therefore avoids contamination of the juice.
Thirdly the juice is separated from the husk and the seeds. With this process we reduce the bitter constituents, obtaining a low reading for quick fibre and a low viscosity in NFC. The resultant juice has a minimum content of the bitter constituents, an agreeable colour, minimum natural oil content and an increased number of intact juice cells. The limonin content is also reduced and the average cell size in the pulp is increased with a higher percentage of floating pulp.
The process does not use water during extraction so that energy consumption is optimised and any contaminants contained in residual water are minimised.
Removing the Bitterness
Once the orange juice has been obtained, it is necessary to remove the bitterness from the juice. This is done by a process designed to eliminate the limonin, naringin and hesperidin compounds from the juice. Specifically for limonin the initial concentration can be as high as 20 ppm, while the target for the final product is less than 0.1 ppm.
The process starts with stabilised fresh juice and 15 Brix reconstituted juice. These are centrifuged in order to separate out the pulp from the juice. Lewait® resin is added to the juice and it is then transferred to a storage vessel where the thermal treatment is carried out.
Treatment of the Pulp and Aseptic Filling
One of the key aspects related to the treatment of the pulp is the mass transfer. HRS Heat Exchangers has developed a piston pump particularly suited to this purpose, a pump which is hygienic and can develop pressures of up to 40 Bar.
Another fundamental aspect of the process is the thermal treatment which is carried out using a triple tube heat exchanger (HRS AS Series). In this heat exchanger the product flows through an annulus formed by tree concentric tubes making the units especially useful for:
- Fluids of high viscosity
- Non-Newtonian fluids
- Fluids which contain small particles
Finally the process uses a “Bag-in-Drum” or “Bag-in-Box” aseptic filler designed by HRS, which allow the product to be packed into aseptic containers. Preformed and pre-sterilised containers of between 5 and 1,000 litres are normally used.
The MI/MR Series Pasteurisers produced by HRS Heat Exchangers are characterised by their high speed of treatment, their ability to carry out product air removal when the product is cold and their low maintenance requirement. Special attention has been paid to the following features:
- Energy recovery. Up to 85% of energy can be recovered which reduces the processing costs substantially.
- Thermal treatment times are reduced. This results in a higher quality product being provided.
- Feature 3. The design is hygienic. This results in a higher quality product being provided. This key aspect of the design is the elimination of all dead zones within the unit where movement of the product is restricted. These zones are inevitable present in traditional designs using product to product heat recovery particularly in the area of the product entry into the headers.
In the case of orange juice production we can take advantage of the MR technology because it allows us to use direct product to product heat recovery. The result is a more compact pasteuriser containing significantly fewer modules. As a result of utilising direct or indirect energy recovery, significant cost savings can be achieved. For example, savings compared to a system using purpose generated steam may be in the region of €220 a day.
CIP Cleaning System
The CIP (Clean in Place) cleaning system used by HRS Heat Exchangers is centralised with automatic control of the parameters. An outstanding feature of this design is that it has automated practically all of the cleaning operations required in the plant.
The principal components in this step are automatic systems for mixing the product, controls for the components and the CIP cleaning operations. Mixing takes place in tanks fitted with agitators in which we can programme the proportions of the various constituents. The mass transfer of the constituents is carried out using centrifugal or piston pumps.
The shipping area contains the chillers used for loading and unloading the tanks. These chillers use HRS MI Series and HRS AS Series heat exchangers that generate the best heat transfer coefficients. The products must be chilled to between 0°C and +2°C.
Drying the Orange Peel
In order to market the orange peel it must be dried. The first part of the drying plant is the hydrolysis zone which takes the peel coming from the juice plant and adds lime (CaO). When we have the hydrolyzed peel it passes to the presses where we obtain a semi-solid product and a liquid. The liquid is passed to a further process of evaporation to produce a concentrated liquid. The semi-solid product and the concentrated liquid are both passed to the final dryer from which comes the dry product. A trommel type dryer can use different types of fuel such as biomass, natural gas etc. and it is important to realise that the exhaust gases from the dryer can be used as an energy source on the evaporation plant. Lastly, the product is passed to a pelletiser which gives the peel in a form which can be sold.