Alison Wailes is a registered dietitian and nutrition consultant to the Canned Food Information Service Inc, 130 Park Street, South Melbourne VIC 3205.
The Canned Food Information Service Inc (CFIS Inc) is an organisation promoting Australian food packaged in steel cans. Through general publicity CFIS Inc aims: to convince consumers and potential consumers of Australian canned food of the merits of this food delivery system and the foods contained, and to dispel misconceptions and so generate increased purchases; to ensure that Australian canned foods remain a regular ingredient in meals rather than an occasional or standby food; and, to influence those canning companies responsible for the choice of future packaging direction in order to create a climate of greater confidence in the future of the steel can.
The CFIS Inc nutrition education program is aimed at increasing the awareness of the influencers of public opinion particularly health professionals and media writers. Canned food has an image problem with both the public and health professionals. A market research survey conducted by the fruit canning industry in 1987 was undertaken to evaluate the attitude of consumers to canned fruit. Two of the key finding were: nutritional balance is important, some canned food is permissible but canned fruits are not very important in many households because they do not connote fresh fruit taste or nutrition to the majority; and, fresh fruit is an important part of almost every household's diet from the nutrition point of view, but it is difficult to select food pieces and as a result fruit is frequently disappointing.
More recently the industry conducted another survey amongst 601 grocery buyers. There were many contradictions in the attitudes of consumers to canned foods particularly what constitutes typical buying patterns. The researchers concluded that canned food is a product category with wide utility, yet one with which few people wish to be associated. The underlying basis for this negativity is concern with nutritional aspects of the product. They found that: the more health/nutrition conscious a person, the more negative he or she was likely to be to canned food; generally younger people were more health and nutrition conscious; and, younger people were correspondingly more negative to canned food, particularly 16–24 year olds.
Similar attitudes exist amongst health professionals, eg the Target on healthy eating which has been used by a number of State Health Commissions in public education programs places canned food generally among the fair choices rather than excellent choices.
Examination of the nutrient composition of canned and, where possible, equivalent fresh food would answer the question of whether these attitudes were justified. Unfortunately at the time these market research studies were undertaken there were very few hard analytical data available on the composition of Australian canned foods in comparison with other available foods.
Nutritional value of canned foods — Study I
In 1988 CFIS Inc commissioned a study to examine the nutrient content of six products, including both fruit and vegetables. The analyses were carried out by the Australian Government Analytical Laboratory, South Australia, a NATA registered laboratory.
This study aimed to compare the nutrient content of food as consumed after undergoing different preparation and processing methods.
Products tested were: pineapple (canned in juice and syrup, and fresh); corn niblets (canned, fresh and frozen); tomatoes (canned and fresh); peaches (canned in natural juice and fresh); orange juice (canned and fresh); pears (canned in natural juice and fresh). Because results applicable to the real world were wanted, the products tested were those available on the market at the time of the study. There was no attempt to match cultivars if this required acquiring samples not available on the retail market at the time. Samples of each product were purchased from six different retail outlets in Adelaide suburbs. The six outlets included three supermarkets, these locations being selected to provide a balance between lower and higher levels on the socio-economic scale. Fresh produce generally was of the cultivars most commonly on sale during January and February. All fruit and vegetables were in good condition and of a ripeness ready for use. The canned products included the major brands available on the Adelaide retail market and were all Australian grown and produced. Generic labelled products were not used.
Composite samples were prepared from equal weights of each can sub-sample after homogenisation. The samples of canned products were prepared using the whole can contents. The fresh food was cooked by the methods considered most commonly employed using measured quantities of sugar and salt to taste as appropriate. The canned products were cooked by heating half the composite sample to 90°C, holding for one minute then cooling. This process was chosen since canned food is already cooked during processing.
In general, standard methods of the American Association of Official Analytical Chemists (AOAC 1984) were used, and full details including modifications to methods appear in the report (CFIS 1988). Riboflavin and thiamin were determined by HPLC using fluorescence detection (Wimalasiri & Wills 1985). Carotenes were determined by reverse phase HPLC after hydrolysis and solvent extraction. Minerals were determined by atomic absorption spectrophotometry of an acid solution following a dry or wet ashing.
Table 1 derived from the study report (CFIS 1988) illustrates the comparison between fresh, fresh cooked, canned, and canned heated peaches.
The moisture levels decreased on cooking, the solids increasing proportionally accounting for the increased energy (kJ) level on cooking and heating. Fat, protein and ash did not differ significantly across all peach products tested. Vitamin C, thiamin, riboflavin and α-carotene were all at similar levels in fresh and canned peaches and both cooked and heated, respectively. β-carotene in both canned and canned heated peaches was comparable with fresh peaches.
In general, there were very few significant differences in nutrient content between fresh, fresh cooked and canned and canned heated products studied. Often the differences that did exist were within the experimental error of the methods used. The exceptions were vitamin C which is heat sensitive, sodium which was added at different levels and nutrients affected by cultivar differences.
Communication to the public
It is notoriously difficult to communicate complex scientific information to the public. So that the information is not distorted, it is important that the message contain a single idea and is expressed simply. The findings from this first study were summarised in the statement that: There were no practical differences between fresh and canned foods in most of the nutrients studied. Even vitamin C was not lost on canning to the extent expected by many people.
Press releases were written around this single message and interest from the media was encouraging. During interviews with the media it was possible to move on from that simple statement to explain more aspects of food processing and its impact on the nutritional value of foods.
Nutritional value of canned food — Study 2
In 1989 CFIS Inc commissioned a second study to examine a range of prepared canned foods. Many of these products have an identity in their own right and are not readily compared with home cooked equivalents.
The Australian canned products tested in this program were: soups: tomato (regular and salt reduced), creamy chicken (regular and salt reduced), cream of pumpkin; entrees: baked beans (regular and salt reduced), spaghetti in tomato sauce with cheese, braised steak and onions; baby food: mixed vegetables (canned), berry flavour yoghurt (canned), fruit of the forest (refrigerated yoghurt). Homemade recipes of pumpkin soup and spaghetti in tomato sauce with cheese were also included.
Because results applicable to the real world were wanted, the products tested were those available on the market at the time of the study. Samples of each product were purchased from different retail outlets in Adelaide suburbs. The canned products purchased included the major brands on the Adelaide retail market and were all Australian produced. The canned products were all prepared according to the directions on the label. Soups were diluted with half milk and half water and heated. The recipes for home made soup and entree were obtained from standard Australian home economics texts.
Moisture and sodium determinations were done on regular and salt-reduced varieties before making composite samples. The composite samples each contained equal weights of each sub-samples after homogenisation. Total can contents were used. As in the first study, AOAC methods of analysis were generally used (CFIS 1988).
The tabulated results which are available (CFIS 1989), cover proximates, carbohydrates, minerals, vitamins and fatty acid profiles. The results also expressed the nutrients in a defined serving size of the product. The serving size has been determined from the labels or from knowledge of current usage. Because each product forms part of a single meal, the amount of each nutrient in the serving size has been compared with the recommended dietary intake for women 19–54 years, men 19–64 years and infants of 6 months of age.
The results showed that each product has specific strengths and to assess the value of these strengths, and express them in a more positive way, a range of criteria were chosen.
The Foods Standard Code of the National Health & Medical Research Council has set limits on the nutritional claims which can be made about particular foods, and a reference quantity of the food must contain a defined portion of the daily allowance of that nutrient. The daily allowances have been derived from the RDIs (National Health and Medical Research Council 1986). In summary the code provisions are: a food may claim the presence of vitamins or minerals if the reference quantity contains one-sixth (16.6%) to one-half (50%) of the daily allowance; a food may claim to be a good source of vitamins or minerals if the reference quantity contains not less than one-half (50%) of the daily allowance; and, a food may claim to be of value in the prevention or cure of disease due to the lack of a vitamin or mineral if the reference quantity contains not less than 100% of the daily allowance.
An alternative criterion is the use of the Nutritional Index (NI). This is an expression of the relative contribution to the RDI of nutrients in a food compared with the contribution of energy value of the food to the energy RDI. People understand the concept of “value for money” and this is similar being nutrient “value for kilojoules”.
The ratio of the percent nutrient contribution to RDI in the serving size to the percent of energy to RDI in the serving is the NI. Where NI > 1 this indicates a higher nutrient contribution than energy contribution of the food in the diet. In Figure 1 the height of the bars for nutrients which are higher than the energy bar indicates NI > 1 and that the food is a useful source of these nutrients.
The Australian dietary guidelines (Commonwealth Department of Health 1981) include the recommendation that the total fat in the diet should be reduced to less than 35% energy. Where NI < 1 for fat this indicates that the food will assist in meeting that goal.
Using these criteria this second study has been able to demonstrate that the canned foods studied make a significant contribution to the RDI of nutrients for adults including young people. Where canned products have been compared with a home cooked equivalent, the differences in composition reflect differences in the recipes rather than differences due to processing.
Table 1. Proximate and vitamin composition of peaches (per 100g)
|Nutrient||Fresh||Fresh cooked||Canned in juice||Canned heated|
|Vitamin C (mg)||5.0||5.0||4.0||5.0|
* ND = Not detected
‡ TR = Trace
Promotional message concerning canned foods
The example for baked beans (Figure 1) can be explained in terms of the range of criteria described above. Thus a typical statement for canned baked beans is: Canned baked beans fit well into the Australian dietary guidelines, they are low in fat, sugar and cholesterol-free. A 125 g serving could claim the presence of fibre and iron and by Nutritional Index criteria is a useful source of protein, complex carbohydrate, potassium, calcium, magnesium, zinc, and thiamin. Reduced salt varieties are also available.
Similar statements can be made about the strengths of all the products tested, ie: soups, entrees and baby foods. Although according to Food Standards Code criteria, claims about the nutrients in these products cannot be legally made, these criteria are useful in illustrating the strength of canned foods. Viewing the nutrients according to the Nutritional Index offers further evidence of the benefits which canned foods can play in a healthy diet. Thus looking at the nutrient profile of a food is more useful than focusing on particular nutrients in isolation.
Communication of results to the public
The scientific information involved in these results is more complex than that involved in the first study. It involves the need to communicate that different products have different strengths whether they are processed or home cooked. In order to communicate this idea, visual bar charts showing a profile of the food are more meaningful than plain figures. It is also possible not only to compare individual foods but to superimpose the food profile so that a combination could illustrate all of the nutrients required. This idea still remains to be tested in the public arena.
Association of Official Analytical Chemists. 1984. Official methods of analysis. 14th ed. Washington DC: Association of Official Analytical Chemist.
Canned Food Information Service Inc. 1988. Residual nutritional value (RNVI). Research and summary report. *
Canned Food Information Service Inc. 1989. Nutritional value research (NVR2). Research and summary report.*
Commonwealth Department of Health. 1981. Dietary guidelines for Australians. J. Food Nutr. 38: 111–9.
National Health & Medical Research Council. 1986. Recommended dietary intakes for use in Australia. Canberra: AGPS.
National Health & Medical Research Council. 1987. Food Standards Code. Canberra: AGPS.
Wimalasiri, P. & Wills, R.B.H. 1985. Simultaneous analysis of thiamin and riboflavin in foods by high-performance liquid chromatography. J. Chromatogr. 38: 412–6.
* Copies available on request from Canned Food Information Service Inc. 130 Park Street, South Melbourne VIC 3205.
Figure 1. Nutrients in canned baked beans (% RDI for adult male, 125 g serving).