Testing the effectiveness of novel MAP techniques

Two industrially funded research clubs were set up at CCFRA to investigate in detail the interesting effects of novel MAP on fresh prepared produce. A High O2 MAP Club ran from April 1995 to September 1997 and as a follow-up, a Novel Gases MAP Club ran from January 1998 to December 1999. These clubs were supported by a total of nine prepared produce suppliers, five gas companies, four packaging film suppliers, three retailers, two suppliers of non-sulphite dips, two manufacturers of MAP machinery and two gas instrument companies.

In addition, further investigations were carried out during a three year EU FAIR funded project, which started in September 1996. The overall objective of this project was to develop safe commercial applications of novel MAP for extending the quality shelf-life of a wide range of fresh prepared produce items. Other aims included investigations of the effects of novel MAP on non-sulphite dipped prepared produce, labile nutritional components and microbial and biochemical spoilage mechanisms. The major focus of this research was on high O2 MAP, followed by Ar MAP, and to a minor extent, N2O MAP.

In summary, the following major results and achievements were made during the course of CCFRA's Club and EU funded novel MAP research:

• High O2 compatible MAP machines were used safely and successfully during the course of the project's experimental trial work. A non-confidential guidelines document on the safe use of high O2 MAP was published (BCGA, 1998).

• Substantial evidence was gathered to demonstrate that undesirable sulphite dips could be replaced by several functional non-sulphite alternatives for inhibiting enzymic discoloration of prepared potatoes, apples and bananas. Several non-sulphite dipping variables (i.e. dip formulations and concentrations, dip temperatures and dip times) were optimised and suitable dipping protocols were recommended.

• Enzymic discolorations of prepared non-sulphite dipped potatoes and apples were generally more effectively inhibited by anaerobic (<2% O2) MAP combinations of N2, Ar and CO2, compared with high O2 MAP. However, high O2 MAP was found to have certain odour and textural benefits for prepared potatoes and apples. Also, high O2 MA packed non-sulphite dipped prepared potatoes and bananas were found to have longer achievable shelf-lives, in comparison with equivalent low O2 (8%) MA packed control samples. For most prepared produce items, under defined storage and packaging conditions, high O2 MAP was found to have beneficial effects on sensory quality in comparison with industry-standard air packing and low O2 MAP. High O2 MAP was found to be effective for extending the achievable shelf-lives of prepared iceberg lettuce, sliced mushrooms, broccoli florets, cos lettuce, baby-leaf spinach, radichio lettuce, lollo rossa lettuce, flat-leaf parsley, cubed swede, coriander, raspberries, strawberries, grapes and oranges (Tables 15.1 and 15.2).

Ar-containing and N2O-containing MAP treatments were found to have negligible, variable or only minor beneficial effects on the sensory quality of several prepared produce items, in comparison with equivalent N2-containing MAP treatments.

High O2 MAs were found to inhibit the growth of several generic groups of bacteria, yeasts and moulds, as well as a range of specific food pathogenic and spoilage microorganisms, namely Aeromonas hydrophila, Salmonella enteritidis, Pseudomonas putida, Rhizopus stolonifer, Botrytis cinerea, Penicillium roqueforti, Penicillium digitatum and Aspergillus niger. High O2 MAs alone were not found to inhibit or stimulate the growth of Pseudomonas fragi, Bacillus cereus, Lactobacillus sake, Yersinia enterocolitica and Listeria monocytogenes, but the addition of 10-30% CO2 inhibited the growth of all these bacteria (e.g. Fig. 15.3 and 15.4).

Ar-containing and N2O-containing MAs were found to have negligible antimicrobial effects on a range of microorganisms, when compared with equivalent N2-containing MAs.

Respiration rates of selected prepared produce items were not found to be significantly affected by high O2 or high Ar MAs, but were substantially reduced by the addition of 10% CO2.

Table 15.1 Overall achievable shelf-life obtained from fresh prepared iceberg lettuce

MAP treatments

Storage days at 8°C to drop to quality grade C

Shelf-life limiting quality attribute(s)

Overall achievable shelf-life

Appearance

Odour

Texture

5% O2/95% N2

4

7

4

Appearance/texture

4 days

5% O2/10% CO2/85% N2

7

7

8

Appearance/odour

7 days

80% O2/20% N2

11

11

11

Appearance/odour/ texture

11 days

Table 15.2 Overall achievable shelf-life obtained from several fresh prepared produce trials

Prepared produce items Overall achievable shelf-life (days) at 8°C

Table 15.2 Overall achievable shelf-life obtained from several fresh prepared produce trials

Prepared produce items Overall achievable shelf-life (days) at 8°C

Industry standard air/low O2 MAP

High O2 MAP

Iceberg lettuce

2-4

4-11

Dipped sliced bananas

2

4

Broccoli florets

2

9

Cos lettuce

3

7

Strawberries

1-2

4

Baby leaf spinach

7

9

Lollo rossa lettuce

4

7

Radicchio lettuce

3

4

Flat leaf parsley

4

9

Coriander

4

7

Cubed swede

3

10

Raspberries

5-7

9

Little gem lettuce

4-8

6-8

Dipped potatoes

2-3

3-6

Baton carrots

3-4

4

Sliced mushrooms

2

Mycelial diameter (mm) 20

Fig. 15.3 Inhibition of fungal growth by different MAs.

Mycelial diameter (mm) 20

AIR

Different gas atmospheres after 6 days at 18° C

Mean fungal area (cm2) per orange after 6 days at 18° C

Mean fungal area (cm2) per orange

21% O2 21% O2 50% O2 50% O2 80% O2 80% O2 0% CO2 20% CO2 0% CO2 20% CO2 0% CO2 20% CO

21% O2 21% O2 50% O2 50% O2 80% O2 80% O2 0% CO2 20% CO2 0% CO2 20% CO2 0% CO2 20% CO

Different gas atmospheres

Fig. 15.4 Inhibition of fungal growth on Penicillium digitatum infected oranges under different MAs.

• High O2 and high Ar MAP did not prevent the enzymic browning of non-sulphite dipped apple slices, but no further browning took place after pack opening.

• Ar-containing MAs were found to inhibit the activity of mushroom polyphenol oxidase (PPO), when compared with equivalent N2-containing MAs. In contrast, no significant inhibition of mushroom PPO activity was found under 80% 02/20% N2 when compared with 20% 02/80% N2. However, the incorporation of 20% C02 into high 02 MAs may inhibit mushroom PPO as well as the activity of other prepared produce PPOs (Sapers, 1993).

• High O2 MAP increased membrane damage of apple slices, whereas high Ar MAP decreased membrane damage. However, apple slices stored under O2-free MAs suffered the most membrane damage, which affected tissue integrity, cell leakage and texture. By comparison, high O2 and high Ar MAP were not found to affect the cell permeability, tissue exudate or pH of prepared carrots adversely.

• High O2 and high Ar MAP were found to have beneficial effects on ascorbic acid retention, indicators of lipid oxidation and inhibition of enzymic browning on prepared lettuce.

• High O2 MAs increased the peroxidase activity of Botrytis cinerea, but the addition of 10% CO2 substantially reduced this activity.

• In comparison with air packing and low O2 MAP, high O2 MAP was not found to decrease single antioxidant (ascorbic acid, b-carotene and lutein) levels preferentially in prepared lettuce but did induce the loss of certain phenolic compounds, even though desirable total antioxidant capacity (TRAP) values after chilled storage were increased.

• Extracts from high O2 MA packed prepared lettuce and onions did not have any cytotoxic effects on human colon cells.

• Ingestion of fresh lettuce resulted in an increase in human plasma TRAP values through the absorption of phenolic compounds and single antioxidant molecules. This increase in human plasma TRAP values was significantly higher than after ingestion of lettuce that had been chilled (5°C) and stored for three days.

• Ingestion of chilled stored lettuce packed under air and high O2 MAs resulted in measurable increases in human plasma TRAP values, whereas virtually no increases in TRAP values were measured after ingestion of equivalent lettuce packed under low O2 MAs.

• A guidelines document was compiled which outlines good manufacturing and handling practices for fresh prepared produce using high O2 MAP and non-sulphite dipping treatments (Day, 2001a).

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