1.Pure juice extract

2.Supernatant of pure juice extract

3.Air dried, powdered and extracted with sterile distilled water

4.Air dried, powdered and extracted with alcohol 

The emergence of new infectious diseases, the resurgence of several infections that appeared to have been controlled and the increase in bacterial resistance have created the necessity for studies directed towards the development of new antimicrobials. Considering the failure to acquire new molecules with antimicrobial

properties from microorganisms, the optimization for screening methods used for the identification of antimicrobials from other natural sources is of great importance. The objective of this study was to evaluate technical variants used in screening methods to determine antibacterial activity of natural products. Thus, a varied range of natural products of plant, fungi and lichen origin were tested against two bacterial species, Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922, by two variants of the agar diffusion method (well and disc), two variants of the bioautographic method (direct and indirect) and by microdilution assay. We concluded that the well-variant of the diffusion method was more sensitive than the disc-variant, whilst the direct-variant of the bioautographic method exhibited a greater sensitivity if compared to indirectvariant. Bioautographic and diffusion techniques were found to have similar sensitivity; however the latter technique provided more suitable conditions for the microbial growth. In this study, we also discussed the best conditions for the determination of minimal inhibitory concentration.

Article Screening methods to determine antibacterial activity of nat...

Pure juice extract and Supernatant of pure juice extract.

Supernatant of the pure juice extract.

I would choose two following methods:

1. Supernatant of pure juice extract (filtered)

2. Pure juice extract (also filtered)

In my opinion, other two methods would not be suitable. In first method you have an alcohol which will be harmful for bacteria, and will probably lead to detection of bactericidal activity of the alcohol itself. With the second method (air drying) you may encounter problem with microbial contaminations. Air drying may leave some spores, and on the other hand, possibly inactivate active compounds from the juice. 

I would advise you to filter the juice before usage. In that case you will be sure of microbiological purity of the material. Make sure that your juice extracts do not contain any contamination.

Good luck with your experiments! 

Extraction with alcohols is mainly used for gathering the phytochemical constituents which are  mostly polar or semi-polar, Although some phytochemicals are polar !. Here, you need to dry the plant part (in shade), This is not  suitable for most fruits which are characterized by high water content (polar  constituents!).

I think it depends on the hypothesis of your study!  

I think, for fruits which are mostly edible, you might want to see if such fruit extracts are able to combat the bacterial infections (Bacteriostatic), so some of them may be recommended as a food supplement during treatment of patients with the proper antibiotic (Bactericidal).

The best way (my own opinion) is  cutting the fresh fruits into small parts  and subjected it to freeze drying, you will get a fresh powder and you can use known weight and concentration in the experiment. If the freeze-drying machine is not available, you can use: "pure juice extract " after filtration. 

You can also mention here the method  that you are going to follow and we can help.

Alcohol extraction is the best suited method to serialize the compound present in various solvent extraction, that could be easy to find out which solvent containing the compound responsible for the activity. Direct fruit juice method can be use but difficult to identify the compounds responsible for.

Last month we conducted a study using antimicrobial effect of fruits. we recommend to use fruit juice with sterile filtration in your research. a very intersiting result will be publish soon !!! 

Garlic has high antibacterial properties on a

wide spectrum of enteric bacteria which could be due to the

chloroform extract or the essential oil of garlic which had

more antibacterial properties than garlic powder against

enteric bacteria [23]. Our study revealed the effectiveness of

the antibacterial properties of garlic juice on enteric bacteria.

Similar to our study results, Saravanan et al. in India

concluded that the aqueous extract of garlic had a great effect

on the target bacteria as the growth of bacteria was inhibited

within 14 h [24]. However, other plants (parsley, celery, mint

and pennywort) did not show significant inhibitory effects on

enteric bacteria which might be due to low concentration of

extracts used or high concentration of bacteria suspension

used. Based on the broth dilution assays, the MIC of 40 mg/

mL could be used as an antibacterial agent against four major

enteric bacteria responsible for gastroenteritis. Our study

confirms the better performance of agar well diffusion

method in the detection of the antimicrobial effects of green

vegetables in comparison with disc diffusion method. In this

experiment, the same concentration of extract and bacterial

suspension was used to avoid bias. The poor performance of

disc method could be attributed to low diffusion of the

extract on the agar surface. Further studies using standard

antibiotics with known concentrations might confirm the

performance of each method.

I agreed with the Hassanain's answer.