Abstract:
A process for treating fruits or vegetables to minimize browning upon subsequent processing, handling, and storage, the method comprising: (a) separating edible pulp tissue from inedible tissue of the fruit or vegetable; (b) blanching said edible pulp tissue in steam for a pre-determined blanching time period at a blanching pressure that is less than or equal to atmospheric pressure; (c) cooling the blanched pulp tissue and extracting residual heat from the blanched pulp tissue; (d) freezing the cooled pulp tissue to obtain at least partially frozen pulp tissue; wherein the frozen pulp tissue obtained from step (d) possesses substantially similar organoleptic properties as freshly separated pulp tissue in (a).

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a process, system and apparatus for treating cut fruits or vegetables such as Avocados that are susceptible to browning or discolouration even during refrigeration. 
       BACKGROUND ART 
       [0002]    Some fruits and vegetables such as the avocado present unique challenges to the food industry. Avocados are particularly unusual because they are highly susceptible to chilling injury. If they are stored at refrigeration temperatures for very long they will discolour and develop off-flavours. Whilst many people throughout the world enjoy eating avocados, difficulties in storing sliced avocado, and the rapid degradation of their desirable organoleptic traits once they are cut, implies that they are not widely used in shelf stable foods. Instead, avocados are largely consumed when freshly cut such as in salads, in sushi, on sandwiches, in guacamole, or simply sliced. Moreover, the known food treatment methods that render most other fruits and vegetables stable further degrades the avocados at an undesirable state. Unless avocados are immediately consumed after slicing, they are difficult to use because their flavour and colour degrades rapidly. This is true whether or not the sliced avocado is maintained at room temperature or at refrigeration temperature. 
         [0003]    Conventional food preservation methods that use heat and pressure tend to activate the native enzymes in the avocado and undesirably affect texture, taste, and appearance of an avocado and likely negatively affect the avocado. Avocados have a high fat content and also contain large amounts of degradative enzymes such as lipases, lipoxygenases, polyphenoloxidase, and methyl pectinases. Once an avocado is sliced the enzymes are released. The enzymes are then able to act upon the fat and other components of the fruit. The enzymes, in particular the lipases, degrade the fats and thus off flavours including rancidity are developed. These enzymes are also responsible for discolouration or browning of the fruit. This browning at least in part is caused due to an enzyme called polyphenoloxidase which is also present in mushrooms, apricots, pears, cherries, peaches, and dates. The polyphenoloxidase (PPO) oxidizes phenolic compounds in the pulp tissue of a fruit and causes condensation to form brown or grey polymers. Whilst in a whole fruit this is not a problem bruising or slicing disrupt cells in the pulp as a result of which the enzymes and the phenolic compounds come into contact with each other and react to form the dark pigments. 
         [0004]    Air also acts to degrade the appearance and the flavour of avocados. The beautiful bright green colour characteristic of a ripe and freshly cut avocado is from the chlorophyll present in the fruit. However, Magnesium in chlorophyll is oxidized upon exposure to the air. Once oxidized, the chlorophyll changes colour from a vibrant green to a brownish green colour. Once again this change of colour is less appetizing in appearance than the bright green of a freshly sliced avocado. 
         [0005]    Therefore, in view of the above shortcomings there has been a long felt need for treating fruits and vegetables such as avocados in a manner that preserves the colour and flavour of fruits such as avocados even after the avocados are sliced, or in the case of guacamole preparation, even after the avocados are macerated. 
         [0006]    The reference to any background information in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge. 
       SUMMARY OF INVENTION 
       [0007]    In one aspect, the invention provides a process for treating fruits or vegetables for minimize browning upon subsequent processing, handling, and storage, the method comprising:
   (a) separating edible pulp tissue from inedible tissue of the fruit or vegetable;   (b) blanching said edible pulp tissue in steam for a pre-determined blanching time period at a blanching pressure that is less than or equal to atmospheric pressure, the blanching time period being less than a cooking time period required to cook the edible pulp tissue;   (c) cooling the blanched pulp tissue and extracting residual heat from the blanched pulp tissue; and   (d) freezing the cooled pulp tissue to obtain at least partially frozen pulp tissue;   
 
         [0012]    wherein the frozen pulp tissue obtained from step (d) possesses substantially similar organoleptic properties as freshly separated pulp tissue in (a). 
         [0013]    Preferably, the blanching time period is less than a cooking time period required to cook the edible pulp tissue. 
         [0014]    As should be relatively clear, the blanching step will preferably take place without directly contacting edible pulp tissue with water by immersion. 
         [0015]    Preferably, a pre-determined volume of steam is used for the said blanching step (b) for a pre-determined volume of edible pulp tissue. 
         [0016]    The steam may circulate about the edible pulp tissue via natural or forced convection currents. Forced convection will typically require a circulation device such as a fan or blower. 
         [0017]    In an embodiment, the process further comprises an additional step of inducing turbulent flow to the steam in the blanching step (b). 
         [0018]    In an embodiment, the process comprises transporting the separated edible tissue on a conveyor apparatus to a blanching chamber for carrying out the blanching step (b). The separated edible tissue is positioned on an endless conveyor belt driven by a conveyor drive mechanism. As a result, the separated edible pulp tissue is passed into the blanching chamber and thereby conveyed in and out of the blanching chamber. 
         [0019]    The operating speed (Cs) of the conveyor belt driven by the drive mechanism may be varied by a control system for controlling a rate of passage of the edible tissue through the blanching chamber. 
         [0020]    In an embodiment, the freezing step (d) comprises rapid freezing of at least an outer surface of the edible tissue. 
         [0021]    In an embodiment, after the cooling step, the cooled and blanched pulp tissue is positioned on a freezing conveyor belt driven by a freezing conveyor drive and passed into a freezing chamber for carrying out the freezing step (d) and for passing the frozen pulp tissue obtained from step (c) out of the freezing chamber. An operating speed (CF) of the freezing conveyor belt driven by the freezing conveyor drive may be varied for controlling a rate of passing the blanched tissue into the freezing chamber. 
         [0022]    In an embodiment, the blanching step (b) is preceded by a segmenting step in which the separated edible tissue from step (a) is segmented into discrete pieces. Preferably, the segmenting is carried out by slicing the edible pulp tissue into the discrete pieces. 
         [0023]    The blanching time period may be in the range of 1-10 minutes, preferably 2-6 minutes and more preferably 3-5 minutes. 
         [0024]    Preferably, the freezing step (d) is carried out for a freezing time period in the range of 2-6 minutes and more preferably 3-5 minutes. In alternative embodiments the freezing step may also be carried out for longer time periods in excess of 6 minutes. 
         [0025]    Preferably the fruit or vegetable is a fresh fruit or vegetable in that the fruit or vegetable has not undergone a freezing process after picking. A preferred fruit is Avocado. 
         [0026]    In another aspect, the invention provides an apparatus for blanching segmented fruits or vegetables, the apparatus comprising: 
         [0027]    a conveyor system for transporting said fruits or vegetables from one end of a blanching chamber to an opposite end, the conveyor system comprising a conveyor belt positioned on two or more drive rollers for transporting said fruits or vegetables and adapted to be driven by a drive mechanism; 
         [0028]    the blanching chamber comprising a shroud overlying the conveyor belt and in longitudinal alignment in relation to the conveyor belt to at least partially enclose steam produced from water in a bath positioned underlying the conveyor belt and in longitudinal alignment with the shroud and the conveyor belt; 
         [0029]    wherein during use the steam produced in the bath is at least partially enclosed by the shroud thereby exposing the segmented fruits or vegetables positioned on the conveyor belt to steam and blanching the fruits and vegetables in the blanching chamber at a blanching pressure that is less than or equal to atmospheric pressure. 
         [0030]    Preferably, the conveyor belt is adapted for allowing passage of steam therethrough from an underside in use position of the conveyor belt to an in use fruit or vegetable supporting surface of the belt. The conveyor belt may comprise perforations for passage of steam therethrough. 
         [0031]    In an embodiment, the apparatus further comprises a control system for varying an in use belt speed of the conveyor belt thereby varying blanching time period of the fruits and vegetables in the blanching chamber. Preferably, the control system is adapted to vary the in use belt speed with reference to one or more parameters relating to the segmented fruits and vegetable positioned on the conveyor belt during use. The control system may also be sufficiently adapted to prevent the in use belt speed from being below a pre-determined value of belt speed. 
         [0032]    In an embodiment, the apparatus further comprises a steam control mechanism for controlling steam volume, steam pressure and/or steam temperature. 
         [0033]    In yet another aspect, the invention provides a system for treating segmented fruits or vegetables upon, the system comprising the apparatus for blanching as described in the preceding sections and further comprising a cooling apparatus positioned for receiving and extracting heat from the blanched fruits or vegetables and a freezing apparatus for receiving the cooled fruits or vegetables for at least partially freezing the segmented fruits or vegetables. 
         [0034]    Without wishing to be bound by theory, it is hypothesized that blanching of the segmented fruits or vegetables for a designated time period as described in the aforementioned sections assists in inhibiting the reaction between PPO and the phenolic compounds present in the edible tissue thereby preventing or at least reducing the extent of browning in the edible tissue. It is also hypothesized that cooling and subsequent freezing of the blanched edible tissue after a designated or threshold time period assists in preventing the initial blanching progressing to complete cooking of the edible pulp tissue while at the same time helps in retaining the browning minimisation effect imparted by the blanching. 
         [0035]    Preferably, the conveyor system transports blanched fruits or vegetables to the cooling apparatus and subsequent to the extraction of heat further transports the cooled fruits or vegetables to the freezing apparatus. 
         [0036]    In an embodiment, the system further comprises a fruit segmenting apparatus for separating edible tissue from inedible tissue of the fruit or vegetable and segmenting the separated edible tissue to obtain segmented fruits or vegetables received into the blanching chamber. Preferably, the fruit segmenting apparatus comprises slicing blades for slicing the separated edible tissue into segmented fruits or vegetables. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0037]      FIG. 1  is a flow chart of the process in accordance with a first embodiment of the present invention. 
           [0038]      FIG. 2A  is a top-down view of an apparatus in accordance with a second embodiment of the present invention. 
           [0039]      FIG. 2B  is a side-elevation view of an apparatus in accordance with the second embodiment of the present invention. 
           [0040]      FIG. 2C  is an end-elevation view of an apparatus in accordance with the second embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0041]    Referring now to the drawings, the process for treating fruits or vegetables in order to minimise browning upon subsequent processing, handling, and storage will be explained in greater detail. 
         [0042]      FIG. 1  refers to a flow chart of a process  100  in accordance with an embodiment of the present invention. In a first ripeness assessment step  110 , whole avocados are classified by using a penetrometer to classify the avocados on the basis of their ripeness. In one preferred assessment, avocados with a ripeness rating of greater than 70 are selected for the process in accordance with the present invention. The selected fruits are then collected on an accumulation counter in an accumulation step  120 . In a subsequent manual handling step  130 , each of the fruits is then sliced into half using a slicing implement such as a sharp knife ( 132 ) and the pit or the seed is manually removed and discarded from each of the selected fruits ( 134 ) and the exocarp/skin is peeled by scooping out the edible/mesocarp of the fruit. The mesocarp is also known as the flesh of the avocado, and this is the edible and most abundant part of the fruit. The edible tissue (which is in two parts-peeled avocado halves) is subsequently transported to a segmenting station  140 . The segmenting station  140  comprises a series of rotating blades which slices and/or dices the mesocarp resulting in segmented pieces of the fruit. The segmented pieces are visually inspected at this stage to ensure that the pieces are separate from each other before being undergoing blanching in a blanching step  150 . 
         [0043]    Referring to  FIGS. 2A, 2B and 2C , a blancher  500  incorporating the present invention is used for the blanching step  150 . The apparatus is mounted on a frame  510  including a plurality of supporting legs  512  and  514  extending vertically. The frames support a conveyor assembly  520  with a conveyor belt in the form of an endless belt  522  supported on rollers (not shown). The frame  510  comprises a shroud in the form of a hood  524  that extends along the longitudinal direction of the endless belt  522  and is positioned to be overlying the endless belt  522 . The hood  524  is structurally configured to be in substantial longitudinal alignment with the endless belt  522 . An elongate bath  526  for containing water is positioned on underside of the endless belt  522  in substantially longitudinal alignment with the hood  524 . The water bath is provided with an inlet means and an outlet means for supplying water and draining water respectively. The hood  524  and the water bath  526  positioned on the overside and underside respectively in relation to the endless belt  526  and together define an interior space of a blanching chamber  528 . In a typical blanching step  150 , the segmented pieces of the fruit from step  140  are positioned on the endless belt  522  at a receiving end  532  of the blancher. A variable speed drive motor  534  is then actuated to drive the endless belt  524  on the rollers. The drive motor  534  is also connected to a control system  536  that controls the speed of the drive motor  534 . The control system  536  comprises a sensory mechanism including sensors that are sufficiently adapted to ascertain parameters such as size, weight etc. of the segmented fruit pieces positioned on the endless belt  524 . The control system  536  processes the parameters and computes an optimal belt speed for passage of the segmented fruit pieces through the blanching chamber  528  in order to ensure suitable blanching. The control system  536  also controls the belt speed such that the belt speed does not fall below a pre-set minimum belt speed. It is important to appreciate that the total time of exposure of the segmented fruit pieces is directly proportional to the belt speed of the endless belt  524 . The time of exposure of the segment fruit pieces to a steam environment is critical to achieving the desired outcome of inhibiting the impact of the ‘browning’ enzyme Polyphenoloxidase (PPO) but not exposing pieces for so long that they tend to ‘cook’. Once the conveyor drive motor  534  is actuated in conjunction with control system  536 , the steam control system  540  is also activated. The steam control system heats the water contained in the bath  526  positioned underneath the endless belt  522 . As the water in the bath  526  is heated, steam is formed and the steam (water vapour molecules) rises due to the formation of convection currents. As the steam starts rising from the bath it passes through the perforations provided in the endless belt  522 . In doing so, the steam contacts the segmented fruit pieces positioned on the belt during the time period (time of exposure/blanching time) of being transported from the receiving end  532  of the blanching chamber  528  to the opposite end of the blanching chamber  528 . The positioning of the hood  524  prevents the rapid escape of the steam and allows the steam to accumulate within the blanching chamber  528 . It is important to appreciate that the structural configuration of the hood  524 , the belt  522  and water bath  528  is such that the pressure in the blanching chamber  528  never exceeds atmospheric pressure. This is achieved by providing a blanching chamber  528  that is not sealed from the atmosphere. Furthermore, the steam used for the blanching process is not pressurised in any manner such by use of nozzles, spraying manifolds etc. before being used for the blanching process of the present invention. 
         [0044]    Upon exiting the blanching chamber the blanched fruit pieces are cooled in a cooling step  160 . This cooling step should be carried out preferably as soon as possible in order to extract heat from the blanched fruit pieces. In the preferred embodiment of the present invention, the blanched fruit pieces exiting the blanching chamber  528  from the exit end  537  of the blancher  500  on the endless belt  522  are then directed into a cooling station  162 . Pre-cooling of the blanched fruit pieces may be carried out by an air chilling mechanism. The air chiller ducts incoming warm moist air surrounding the blanched fruit pieces and releases cooled dry air. The pre-cooling step assists in removing any water that may have inadvertently condensed on the surface of the avocado pieces. The pre-cooling step  160  is introduced prior to a freezing step to lower the heat coefficient and increase freezing efficiency. This is predicated primarily on commercial reasoning to lower the gas usage cost of IQF freezing at the subsequent station. 
         [0045]    After the pre-cooling step is conducted, the pre-cooled avocado fruit pieces are transported out of the pre-cooling station  162  and subsequently transported into a freezing station in the form of an Independent Quick Frozen (IQF) tunnel  172  to carry out a freezing step  170 . The primary goal of the freezing step  170  is to freeze the avocado pieces as fast as possible in order to minimise water crystallisation of the cut surfaces and produce a final frozen product that comprises substantially similar organoleptic characteristics as that of fresh-cut avocado. To achieve this, Independent Quick Frozen (IQF) freezing technology is used, with carbon dioxide (CO 2 ) being identified as the preferred refrigerating freezing gas. The endless belt  524  carries the avocado pieces from the pre-cooler station  162  into the IQF freezing tunnel for a pre-determined freezing exposure time. The preferable temperature for freezing the avocado pieces is from −10° F. to −150° F., and more preferably from −70° F. to −120° F. If the temperature is too low, the avocado pieces cannot endure such low temperature and cracks or fissures might be caused. If the temperature is too high, it takes too much time to freeze resulting in an inefficient operation. The extent of exposure of the cooled avocado pieces is determined by the belt speed of the conveyor belt when it is passing the IQF freezing tunnel  172 . In one preferred operating configuration, the belt speed of the endless belt  522  may be controlled to be the same as the belt speed used during the blanching step. However, in alternative configurations, the belt speed may be varied using the control system  534 . The freezing step must at least be carried out for a sufficient time period that results in formation of at least a ‘crust’ freeze on each of the avocado piece subjected to the freezing step  170 . Subsequent internal (core) freezing may be carried out in later steps. Alternatively, the freezing step  170  may also be carried out for a longer time period to ensure complete freezing in the IQF freezing tunnel  172 . The requirement of at least carrying out crust freezing limit the extent to which avocado pieces stick to each other, which is an important consideration. Rapid freezing is an important step because fruits such as avocado consist of cells that are filled with water, so that the simple freezing convection (gas or liquid) causes the water to freeze forming ice crystals disrupting the structure and cracking the cell walls of the fruit. By subsequently thawing of the fruit or vegetable that is frozen by simple freezing, the water comes out through the cracked cell walls, leaving a texture that is aesthetically not appealing. The faster the fruit is frozen, smaller the water crystals; thus less disrupting the cell walls, wherewith less liquid is released when thawing. 
         [0046]    After the conclusion of freezing step  170 , the frozen fruit pieces exit the IQF tunnel  172  on the endless belt  522  and reach a packaging station  180 . The packaging step  180  mainly requires the use of suitable packaging such as vacuum seal packaging to prevent the exposure of the frozen fruit pieces to ambient conditions in order to avoid contamination. Any other alternative forms of packaging may also be used in further advantageous embodiments for avoiding contamination. Another important requirement is to limit exposure of the frozen fruit pieces to UV light in order to avoid pigment fading. The sealed fruit pieces may be further packaged into storage containers such as carton boxes in a further packaging step  185  before being stored in cold storage in a conventional cold storage facility  190 . 
         [0047]    The frozen avocados produced by conventional methods easily disintegrate and discolour rapidly at the time of thawing or they are very expensive. However, the frozen avocado pieces produced according to the process of the present invention can preserve their integration, shape and colour for a period of more than  2  weeks after thawing. Moreover, the taste of the avocado pieces thus produced is maintained in a good condition. 
       EXAMPLE 1 
       [0048]    In accordance with the ripeness assessment step  110  described in earlier sections ripeness assessment of a batch of avocados with a combined weight of 5 kgs was carried out using a penetrometer and all fruits with a ripeness of greater than 70 N were selected. The fruits were subjected to steps  110  to  140  in accordance with the present invention to obtain sliced fruit pieces. Half of the sliced fruit pieces were segregated for the blanching, pre-cooling and freezing steps in accordance with the process of the present invention and the other half was marked as a TEST batch and was left untreated after being sliced into smaller pieces and used a comparative example. Any fruit with exocarp (skin) that had been penetrated, was not selected. The temperature of the core of the fruits was recorded to be in the range of 9-12° C. 
         [0049]    At the end of the segmentation step  140 , the segmented pieces were visually inspected by personnel and aligned on the endless belt  522  for maximum orientation with dimensions of the endless belt  522 . The width and length of the endless belt  522  used in Example 1 were 900 mm and 3.5 m respectively. Blanching was carried in accordance with the blanching step  150  for blanching time period of 3-5 minutes. The belt speed was adjusted using the control system  534  in order to ensure that the segmented avocado pieces passed through the blanching chamber  528  for the time period of 3-5minutes. After the blanching step, the pre-cooling step  160  was carried out to reduce the temperature of the blanched avocado pieces to a temperature in the range of 20-25° C. After the pre-cooling step, the cooled avocado pieces were subjected to ICQ freezing in the IQF tunnel in accordance with the rapid cooling step  170  for a freezing time period of 5 minutes. 
         [0050]    With respect to the shape of the avocado pieces, it was observed that the original shape of each avocado pieces from Example 1 was preserved on and after thawing. In relation to any visually observable colour changes, no significant change was observed until at least ten days with some individual pieces retaining their original colour for as long as 14 days. Thereafter, the surface of the avocado pieces was observed to become gradually blackened due to oxidization. 
         [0051]    The taste of the thawed avocado pieces was good enough for eating. Furthermore, long term tests carried out for a 12 month period have also indicated that the pieces retained their colour taste and other desired organoleptic properties once they were thawed after being kept in frozen storage for 12 months. 
         [0052]    The frozen avocados from the untreated batch (the comparative example) easily disintegrate and discolour rapidly at the time of thawing. However, the frozen avocado pieces produced according to the present invention can preserve their integration, shape and colour for almost 2 weeks after thawing. Moreover, the taste of the avocado pieces thus produced is maintained in a good condition. 
         [0053]    Throughout the specification, the terms “edible tissue”, “pulp tissue” and “pulp” refer to the mesocarp of the fruit which is generally the succulent and fleshy middle layer a fruit located in between the pericarp (the outer skin) and the endocarp (the seed). The mesocarp is usually the major part of the fruit that is eaten, for example, mesocarp makes up most of the edible part of an avocado. Therefore these terms may refer to the fleshy edible regions of any fruit. 
         [0054]    In the present specification and claims (if any), the word ‘comprising’ and its derivatives including ‘comprises’ and ‘comprise’ include each of the stated integers but does not exclude the inclusion of one or more further integers. 
         [0055]    Reference throughout this specification to ‘one embodiment’ or ‘an embodiment’ means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations. 
         [0056]    In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.