Design and Maintenance of Green House 3(2+1)

Lesson 30 Post -Harvest Quality of Greenhouse Produce

30.2 QUALITY ATTRIBUTES

• The quality is a combination of attributes, properties or characteristics that provide the product value, depending on the destined use.  

• The appearance, the texture, the firmness, the organoleptic characteristics and the nutritional value are components of the quality.

• The  relative importance of each  component of the  quality  depends on  the  product and  how  it  is consumed, varying among growers, distributors  and   consumers.  

• For   the   grower,  a product must provide high  yields and  have a  good   appearance, be  easy   to  grow  and have  a good  resistance to transportation, whereas for  the  wholesaler the  qualitative attributes of appearance, firmness and  shelf life  prevail.

• In addition, the consumer values the healthiness and the   nutritional value. In general, consumers place a high value on fresh   fruits and   vegetables as a healthy and natural food.

• Many of the qualitative attributes of fresh horticultural products are   subjective, which makes their evaluation even more complex.

• The  consumer usually judges the quality of a product by its external  appearance and, if  there is  no  other information (different production  methods,   differentiating  labels),  will deduce that a  product  with  a  good   appearance will  have  a good  internal quality.

• The colour, the size, the uniformity and the absence of defects are basic aspects of the appearance, together with a good presentation, in proper packages that contain a standardized product.

• The food safety and hygiene in the production process demanded by the consumer have made necessary the establishment of rigorous production protocols (which specify growing methods, traceability, etc.) that guarantee the healthiness of the products.

• Transport over  long  distances in  some cases  means that  some  vegetables are  harvested before the commercial ripening point; so that  when they  reach the  consumer they are in a suboptimal organoleptic condition.

• The greenhouse growing conditions (light, temperature, irrigation, nutrition, salinity) affect the quality (Welles, 1999), so their management must be optimized.

• The qualitative attributes of vegetables vary with the species. In some   products such as cucumber, whose shelf life is the main quality attribute, a qualitative evaluation is simple, whereas for others such as tomato, it is more complicated, especially regarding its organoleptic characteristics.

• In some cases, such as tomato, achieving a high quality may involve a decrease in the yield, so a compromise between quality and quantity in the production must be reached.

• The sensorial quality is dictated by a number of external and internal factors. The  external factors include the  attributes related to  the  appearance, such as  colour, form,  size  and  firmness, and  are subject to physical and  visual properties, being appreciated by  the  consumer through the senses of sight  and  touch, whereas the attributes related to flavour, aroma and  texture,   which are  sensed by  the   taste   and smell, are included among the internal factors  of sensorial quality (Martínez-Madrid et al., 2000).

• The   essential criteria to evaluate the sensorial quality in fruits and   vegetables are the colour, flavour, aroma and texture. The   flavour and the aroma are the most subjective and difficult to evaluate qualitative aspects.

• The flavour can be evaluated by taste and smell, and is mainly composed of sweetness, acidity and aroma, that correspond to the sugars, acids and volatiles, respectively (Baldwin, 2003).  Other components of the flavour are bitterness, salinity and   astringency.

• The   acidity and the aroma modify the perception of sweetness, one of the most important components of the flavour in fruits and vegetables. The perception of the  non-volatile components of  flavour  (sweet,  acid,  salty   and   bitter) takes  place on  the  tongue and  the  aromas are  detected by the  nose;  both  perceptions are integrated in the brain, being  difficult to distinguish between them (Baldwin, 2003).

• The genetic characteristics are the main determinants of flavour and  aroma of fresh horticultural  products,  although they   are influenced, but  to  a lesser degree, by  cultural practices and   the  pre-harvest conditions, as  well   as  by  the  ripening stage  at harvest and  any subsequent handling.

• The  organoleptic quality of non-climacteric fruits generally decreases after harvest,  whereas  climacteric  fruits  may reach  their  best   quality  after   being   harvested, if they  are harvested after the beginning  of the ripening process.

• The sensorial evaluation of flavour and aroma of a product is usually done by taster panels. Consumer preferences vary depending   on   socio-economic, ethnic and   geographical conditions.

• The sugars that supply the sweet flavour are fructose (the sweetest), sucrose and glucose (the   least   sweet). Organic acids, such as citric acid in tomato, provide the acid taste.

• In  the  majority of melon cultivars the main sugar is sucrose and  the most common acids are citric and  malic acids, whereas in watermelon sucrose predominates and, in some  cultivars, there are high  levels of fructose,   and   malic acid   is  the  only   relevant acid  (Baldwin, 2003).

• In tomato, the total content of soluble solids and the acidity determine its taste. The most abundant sugars are glucose and fructose, at approximately equal levels, with citric acid being present in greater quantities than malic acid. There is also  the  presence of a large number of volatile compounds (more  than 400)  from  which 16  contribute more  effectively to the taste  and  aroma (Baldwin, 2003).

• The  texture is a qualitative attribute that is critical for the  acceptance of fruits and  vegetables, that  is, for the  perception that  the  consumer has  of  the  qualitative characteristics. The texture involves the structural and mechanical properties of an edible product and its sensorial perception in the hand or in the mouth (Abbot and Harker, 2003).  

• The texture is related to a series of chemical compounds responsible for the perception of the structure, such as pectin, cellulose, hemi-celluloses and proteins (Martínez-Madrid et al., 2000).

• Sometimes, the term texture includes some mechanical properties, which cannot be of interest to the consumer, such as resistance to mechanical damage or transport. The texture is altered throughout the shelf life of the product, so it can only be referred to at the time of evaluation.

• Measurements of texture, nowadays, are   considered critical indicators of the non-visual aspects of quality. The complexity of the texture allows for its complete measurement only   by means of sensorial evaluation (valuation panels), although instrumental measurements are preferable, whenever possible. There are many measurements that relate to textural attributes, normally the more precise ones being those that use destructive methods (Abbot   and Harker, 2003).

• Obtaining a  high  quality product depends on  the  expression of  the  genetic characteristics of the  chosen cultivar under the   ecological conditions  in   which  it  is cultivated.

• The study of the nutritional value and the beneficial effects of fruits and vegetables on human health has become increasingly relevant in   recent years   (Desjardins and Patil, 2007; Patil  et al., 2009).

• The  control of the  pre-harvest conditions, of  an  environmental  nature  (temperature, humidity,  radiation,  soil,   rain) and  cultural nature (nutrition, irrigation, pruning), is not  enough to achieve a good quality product, as  the  ripening stage  of the  fruits at  the  time  of harvesting is  the factor  that   plays an  essential role  in  the sensorial qualitative characteristics. This is  because the  production of  compounds such as  the  aromas that  contribute to  the flavour take place, mainly, in the advanced stages of  the  ripening process (Martínez- Madrid et al., 2000).

• An early  harvest has advantages for distribution of  the  product, as  the  texture is maintained for  a  longer period extending the  shelf  life,  but  this  is  to  the  detriment of its sensorial quality, at least  in non- climacteric fruits.

It is evident that the future relies on the quality, but is must be economically feasible quality. The fixing   of integral quality systems is a clear priority in the production of greenhouse vegetables.

30.3 QUALITY CONTROL AND ASSURANCE

Quality control (QC) is the process of maintaining an acceptable quality level to the consumer. Quality assurance (QA) is the system whose purpose is to assure that the overall QC job is being done effectively (Hubbard, 1999). QA and QC are often used interchangeably to cover the planning, development, and implementation of inspection and testing techniques; they take time and a lot of training. A successful QA/QC system cannot  be  flexible,  but  it  must  be  subject  to  constant  review  and  improvement  as conditions change (Hubbard, 1999).

Many attempts are currently being made to automate the separation of a given commodity into various grades and the elimination of defective units. The availability of low-cost microcomputers and solid-state imaging systems has made computer-aided video inspection on the packing line a practical reality. Solid-state video camera or light reflectance systems are used for detection of external defects, and x-ray or light transmittance systems are used for detecting internal defects (Abbott et al, 1997; NRAES,1997). Further development of these and other systems to provide greater reliability and efficiency will be very helpful in quality control efforts.

An effective quality control and assurance system throughout the handling steps between harvest and retail display (Table 30.1) is required to provide a consistently good- quality supply of fresh horticultural crops to the consumers and to protect the reputation of a given marketing label. Quality control starts in the field with the selection of the proper time to harvest for maximum quality. Careful harvesting is essential to minimize physical injuries and maintain quality. Each subsequent step after harvest has the potential to either maintain or reduce quality; few postharvest procedures can improve the quality of  individual  units  of  the  commodity  (Cavalieri,  1999;  Kader,  1988;  Kader,  1992; Shewfelt et al., 1993).

Exposure  of  a   commodity to temperatures, relative humidity,  and/or concentrations of oxygen, carbon dioxide, and ethylene outside its optimum ranges will accelerate loss of all quality attributes. The loss of flavor and nutritional quality of fresh intact or cut fruits and vegetables occurs at a faster rate than the loss of textural and appearance quality. Thus, QC/QA programs should be based on all quality attributes and not only on appearance factors as often is the case. More research is needed to identify the reasons for the faster loss of flavor than appearance quality and to develop new strategies for extending postharvest-life based on flavor to match that based on appearance.

Table 30.1 Quality assurance procedures during handling of horticultural perishables.

Handling steps	Quality Assurance Procedure
Harvesting	Training workers on proper maturity and quality selection, careful handling, and protecting produce from sun exposure.
Packing house operations	Checking product maturity, quality, and temperature upon arrival. Implementing an effective sanitation program to reduce microbial load. Checking packaging materials and shipping containers to ensure they meet specifications. Training workers on proper grading by quality (defects, colour, and size), packing, and other packinghouse operations. Inspecting a random sample of the packed product to ensure that it meets grade specification. Monitoring product temperature to assure completion of the cooling process. Maintaining effective communications with quality inspectors and receivers to correct any deficiencies as soon as they are identified.
Transportation	Inspecting   all   transport   vehicles   before   loading for functionality and cleanliness. Training workers on proper loading and placement of temperature-recording devices in each load. Keeping records of all shipments as part of the “trace- back” system
Handling at destination	Checking product quality upon receipt and moving it quickly to the appropriate storage area. Shipping product from distribution center to retail markets without delay and on a first in/first out basis unless its condition necessitates a different order.

 

30.4 STANDARDIZATION AND INSPECTION OF FRESH PRODUCE

Grade standards identify the degrees of quality in a commodity that are the basis of its usability and value. Such standards, if enforced properly, are essential tools of quality assurance during marketing and provide a common language for trade among growers, handlers, processors, and receivers at terminal markets. Some production areas like California, USA enforce minimum standards concerning produce quality, maturity, container, marking, size and packing requirements. This provides orderly marketing and equity in the marketplace and protects consumers from inedible and poor quality produce.

Inspection is done either on a continuous basis (where one or more inspectors are assigned to a packing house to make frequent quality checks of the commodity along the packing lines), or on a sample basis (where representative samples of a prescribed number of boxes out of a given lot are randomly selected and inspected to determine whether the product meets the grade specification for which it is packed). When inspection is completed, certificates are issued by the inspector on the basis of applicable official standards.

To  ensure  uniformity  of  inspection:  1)  inspectors  are  trained  to  apply the standards, (2) visual aids (color charts, models, diagrams, photographs and the like) are used whenever possible, (3) objective methods for determining quality and maturity are used whenever feasible and practical, and (4) good working environments with proper lighting are provided.

International standards for fruits and vegetables were introduced by the Organization for Economic Cooperation and Development beginning in 1961, and now there are standards for about 40 commodities. Each includes three quality classes with appropriate tolerances: Extra class = superior quality (equivalent to “U.S. Fancy”); Class I = good quality (equivalent to “U.S. No. 1”); and Class II = marketable quality (equivalent to “U.S. No. 2”). Class I covers the bulk of produce entering into international trade. These standards or their equivalents are mandatory in the European Union countries for imported and exported fruits and vegetables.

REFERENCES

1. A.A.Kader, 2001. “Quality assurance of harvested horticultural perishables” Proceedings of 4^th  International Conference on Postharvest. 553, ISHS.

 2. Nicolas Castilla, 2013. “Greenhouse Technology and Management.” Ediciones Mundi-Prensa, Madrid (Spain) and Mexico.PP. 245-246